Seems a bit silly to have multiple tanking specs for one class. Warriors have just protection, Paladins have just protection, and Druids have just feral. I'm pretty sure it's all but set in stone that Unholy is going to be PvP/DPS, Blood to be PvE/DPS, and Frost to be tanking/cc. I'm pretty sure that hero classes aren't particularly different, just more special.

Frost makes sense for tanking because it's more focused on survivability just like it is for mages. Frost Presence increases armor just like a mage's Frost Armor does.

All that said, it's not like every DK tank spec is going to be 0/0/71. It's most likely going to utilize talents from another tree, probably Unholy but that's just my opinion based on the very little knowledge we have so far, just like Druid tanks use some Resto talents and Paladin tanks use some Ret talents.

@Hurode

Yeah, I think it's a bit silly as well. Without disclosing too much, I can say that none of the DK trees resemble standard "tanking" trees... mitigation talents and threat talents kind of strewn all over, and at all levels. Spell damage and attack power and disease effect modifiers everywhere as well.

I'm really quite ambivalent about what I've seen thus far. I WANT to tank with my DK, but God knows how the hell I'm supposed to do that efficiently.

I'm not sure how terribly useful the alpha talent trees are, but if the Death Knight uses DPS to hold aggro, he could have multiple possible tank builds to specialize for raiding by using certain talents within trees designed for a broader range of skills (like bear form as part of the feral tree, which is also a melee DPS tree if talents are used differently). Right now, each of the tanks is better or worse at certain types of tank jobs, but all will work in most small groups. If a DK can specialize to be more like a bear tank, or more like a paladin tank, or more like a warrior tank it could well become the "offtank class" (which was sort of alluded to when Blizzard called it the Magic Damage tank).