I loved Blood DPS. And I still think Frost should have been the tank spec, but that's a dead conversation.

Until recently I had never even thought about touching Frost. The only reason I have now is because a friend got me hooked on PvP, and my guild's arena team is forced to run with two dks. He is going Blood, so I decided to try Frost. I will say, even though it is based alot on RNG, it feels so much easier to play Frost than Unholy. And don't even get me started on the PvP side. HC is a reset button, and I have more to do as Blood than as Frost, and thats not the survivability part.

And now I am anti-frost ranting so I will just stop right there.

I don't know DKs very well but I thought this is the reasoning behind disrepancy of dps, at least for warlocks in the early tiers of Wrath:

You might have a higher theoretical DPS, but it comes at the expense of a more difficult rotation (e.g. affliction warlock rotation was unforgiving, but it does give you higher dps if played perfectly).

Now, at the hands of a skilled player, the harder rotation does give higher dps, but if that skilled played decides to play for the more fun spec (lower dps, easier rotation, but more fun for whatever definition of fun) then that played would have had extra "attention" to kite adds, stun adds, or whatever else the gimmick of the fights may require.

For a less skilled player, they can play either the best spec but suboptimally (missing procs, mis-timed things, etc) or play the second best spec but it would take their entire attention.

I love Arcane, I have played arcane since beta. I enjoy frost and sometimes I play it for fun, pvp or cc. I can't stand fire for some wierd reason, but I'm still pushed to run fire OS in raids because of the AoE. I don't think its 100% the players choosing the technically better dps spec, I think its the pressure of the raid (I'm saying this all relative to mages, but thats because I'm a mage, it works for everything) making players change. Before arcane was balanced (and I see we are unbalancing it a little, I want to run the numbers, but a lot of players switching doesn't seem to be a problem to me as 90% of raid mages ran fire, and a good amount didn't want to, you gave them the option to go something else, so they did) if you do badly with a good spec, you messed up, oh no, get em next time, improve played. But if you do badly as a "bad" spec, you will get kicked, yelled at, etc. because its seen as you making a choice to simply be a worse player for the raid.

I think the real answer is to balance them in a whole new way, make them all good at different things. I don't mind playing the cc and AoE specs because it gives me something new to do and learn, I get to try something new. Thats what it should be, all specs shouldn't be all good at the same thing (though if the content pushes the one role maybe they should all be somewhat good at it), one should be good at one thing, the other at another, then you can vary them. Maybe we still will choose the same main spec and then vary the OS but at least it gets more interesting. If I play arcane, I don't want to be forced to change permanently, if I play arcane I don't want a scorch like spell (something for movement is nice, but not the same thing). We shouldn't be focusing on each spec is good at the same stuff, because what are we doing? We are just changing the colors of the spells.

Yes, but... if specs get close enough, it becomes debatable which one actually provides the higher DPS. Different simcrafters will end up coming up with different answers, depending on the assumptions. There does reach a point where people who absolutely must hop to the highest spec for that 1% difference won't all be hopping in the same direction, and everyone else will just play what they like best (and probably do at least 1% better because of it).

My DK was blood DPS until Cataclysm, I liked the self-healing. Come Cataclysm I went frost and I really love it now. Frost is probably OP for kiting things! I'm sad about the Dark Succor glyph nerf though, I loved being able to take pressure off healers by Death Striking.

As for specs, for me it's a) DPS and b) not a pet class, so frost was obvious (and should have been obvious from the beginning - when I was blood DPS my spec avoided blood parasites and dancing rune weapon! I don't like pets).

I think for the majority of players, if the difference in theoretical damage is any more than 2-3%, most players will (although some begrudgingly) respec en masse.
Although there are a few out there, myself included, that will almost NEVER switch from their favorite spec, unless it truly becomes broken (eg frost mage in pve). I've played an AffLock since the start of wrath, and even through Ulduar and ICC, when destro locks were OP and a dime a dozen, i never even thought about respeccing. I just have WAY too much fun playing afflic. My guild used to ask me to respec, until i constantly beat out any destro lock that grouped with us, most of whom were better geared than I. To me its all about knowing your spec and playing it well. A truly skilled player playing a sub-par spec will still beat an average one playing an OP spec.

While I have characters of every race and class (and profession; I can only stand to craft if I can be self-sufficient), the only classes I can stand to play, long term, are Paladins and Druids, due to the fact both of them can fulfill all roles; while I can amuse myself with other characters, I'm not really willing to dedicate myself to a character that can't both tank and heal.
Which, in turn, means I have no choice of specs, as the role I have to fill also mandates the spec.
This, BTW, is one thing that makes me tempted to go play Rift instead of WoW. 5 stored specs (compared to WoW's 2), and 8 "trees" for each class (compared to WoW's 3), means I would have much more choice with a single character. Besides, the fact that all classes can at least dabble in tanking and healing makes me willing to give a try to all of them.

I think "majority" is an overstatement. Unless you meant the majority of top guild, striving-for-realm-firsts players. Which spec the average player chooses to play is a lot more complex than simply choosing the one with the highest theoretical dps, especially if the difference is only a few percent.

Some people play their favorite spec no matter what, or they stick to the spec they leveled with because they are so familiar with it. I think that's why I saw so many Frost mages and BM hunters during Wrath, when those specs were not considered raid viable.

Some people try out different specs and settle on the one that is easiest to play. During Wrath I personally saw many more Blood dks than Unholy. My theory was that Blood had a strict, memorizable rotation, so was easier to play, so more people played it. Prior to 4.1 I saw nearly as many Arcane mages as Fire mages, even though Arcane was pretty terrible dps-wise. Maybe because it has an easy rotation (not that Fire's is hard). Maybe because people didn't want to switch from the spec they'd played during Warth (when it was both easy and best dps).

Maybe they just like gattling gun arcane missiles.

I am with you on blood spec. I loved it and played it well. I could do way more dps in blood than any other spec. Why Blizz decided to make blood the tanking spec is beyond me. 2H unholy feels like a melee hunter - having to watch that stupid ghoul pet is not my idea of fun. Dual frost is like a rogue in plate - if I wanted to play a rogue I would play a rogue! I want my old blood DK back, with a big ol 2h weapon. It is very tiring to keep having these "little" changes made. Just when I get happy with a play style, Bliz decides the make a "small" change that completely changes the way a class is played. I have a lvl 85 of every class and I have pretty much retired my DK. I play a shadow priest, for now, but with the nerfs incoming on that class - and yet another play style change, it may be time to switch to my hunter... again.

It is not the players themselves that are choosing the less fun specs, but those that they play with. I would personally choose my favorite spec, weapons, armor, and everything else, regardless of damage, as long as I was running solo.

But if spec X does .00001% more damage, on average, than spec Y, you better be running spec X if you ever want to get invited to a group.

I'm a hunter. I've tried beast mastery, survival, and marksman. And I've gone back to being a beast master hunter now that I'm in a raid with a leader that doesn't care what spec you are as long as the raid does well. I love the way BM feels, I love the lore/roleplay that I can get out of it (I'm an RPer and raider both) and I'd rather play what I like, rather than have my nose pressed to the grindstone of numbers and "profit".

If you're in a raid that insists you change specs because you're not in the spec that does the most DPS for that class, at least consider looking for a new raid. Chances are you'll be happier.

I'd rather have a job I love that pays enough to get by vs. one that I hate but that makes me rich, too.

I disagree with 0% I for one think that that is what the dual spec-ing is all about for only dps players. I have a hunter that is way more fun as a beast master and i refused to change it even when it was numerically better to be Marksman or Survival. I just think that it has to actually be more fun. not just in theory but in reality.