Blessing of Kings does a great job with this post of putting into words (and then extending) the idea of something we've talked about many times before: all guilds are not equal. He separates them into a kind of hierarchical class structure, with "Royalty" (guilds like Stars and Ensidia) at the top of the raiding game, going down to "Aristocracy" (guilds working on hard modes), "Gentry" (guilds who've cleared normal but haven't been able to do hard modes yet), "Bourgeoisie" (guilds working on normal), and the "Proletariat" (casual folks who haven't started raiding). I think he's squeezed things down a bit farther than he should -- I would call the "Bourgeoisie" level guilds still working on Ulduar and Naxx normal fights, as I think there are quite a few of those out there. But his points are strong -- there are bands of raiding guilds, partly by Blizzard's design and partly by mere fact that people approach the content in their own ways.
This whole list was brought up by the old argument of whether or not WoW is too easy, something that seems to come up periodically, especially whenever a new tier of content is released. Actually, we're talking about whether raiding is too easy here, and BoK says that there are too many people in the "Gentry" category he defines -- too many people who've finished off normal modes, and who seem to think that hard modes just aren't for them. I guess the solution there, besides, you know, more content, is that instead of making a huge difficultly ramp from normal to hard modes, Blizzard should tweak up the difficulty of the last few bosses in normal, giving "the Gentry" a chance to get a taste of tougher content before they move up into the hard mode tier.
The good news is that at this point, we're really talking about variations on a boss level rather than an entire dungeon -- back when Naxx was originally dropped into the game, the problem was that no one could run any of it unless they were in the upper level "Aristocracy," and Blizzard has certainly fixed that problem. I think in the future that we will see even more levels of difficulty. I'm not convinced that Blizzard will stick with the 10/25/normal/Heroic model (in fact, we've already heard that the toggle will mix things up in Icecrown), but I'm sure they'll continue to give us more and more ways to run content the way we want, rather than moving through a required order or gateway.