Why is Invincible only available to 25-player raids? (Source)
Blizzard loves 10-person content guilds just as much as we love 25-person content guilds. The reason for having this mount in the 25-person Lich King encounter has to do with maintaining the proper distribution of such awesomeness. If it were available in the 10-person encounter as well, it may be come too prolific and lose some of its initial unique qualities.
Talent changes in Cataclysm (Source)
I was going to bump this to the General forum, but I think the talent tree comment is worth addressing in the role forums, since it applies to class design.
1) We are changing talent trees, in some cases substantially. The major focus is pruning out boring but valuable talents that passively increase say damage or healing.
2) A secondary focus is to fix the clunky areas (e.g. warlocks having two conflicting range increasing talents). We're not going to remove old favorites or radically change the focus of the trees. You will definitely have to rethink your builds however.
3) Because you earn passive bonuses just for spending points in the tree, those fun, niche or utility talents won't seem as expensive as they do today. We want to create a lot more choices where you are choosing utility vs. utility. We want to see far more "cookie cutter" build guides that say "Spend the last 5-10 points where you want."
4) In some cases, trees will flat out get new abilities. These are in addition to the new level 81 abilities.
5) You will get 5 additional talent points for the new levels.
6) We are not deepening the trees. This actually unlocks some interesting opportunities. For the first time, you can reach a 51 point talent and a 21 point talent in another tree.
I'll also add that for Lich King we just brought Naxxramas back and adjusted the bosses for 10 and 25 raid sizes. The Cataclysm raids are new content with new maps and new bosses. We're just trying to hit the nostalgia button with mentioning old foes like Ragnaros. Ragnaros may be back, but he's not in Molten Core.
Purified Lunar Dust (Source)
It is about 22 spell power under budget, and will be fixed.
Top DPS specs on Professor Putricide (Source)
I think one of the most interesting aspects is to look at those classes where one spec is generally perceived to be "the best."
For rogues, locks and hunters there are some players who choose the "second" spec even at a presumed dps loss. For mages, nearly all go Arcane even though Fire's damage really isn't that bad. (What I mean is that I don't think you can argue Combat, Survival and Destruction all trump Fire to explain why there are more of those specs on this fight). In all four cases, the third spec is pretty dead. (We'll assume the Demo locks are mostly there for DP, which as I've said before is not ideal).
Keep the encounter in mind, too. Putricide is a fight where standing still is heavily penalized, yet healing is also not as much of a bottleneck as is damage. We see a lot of groups have a healer go dps for example, which might boost e.g. the Elemental and Shadow numbers just for this fight.
Death Knight
Death Knight tank representation (Source)
There are still plenty of DK tanks in Icecrown.
The death knight was a new class with a lot of cool abilities, lore and a great starting experience. It doesn't surprise me at all that a lot of players flocked to them. When it turned out they were overpowered in dps, PvP and tanking early on in Lich King, that probably encouraged more players to pick them up or stick with them. So it's natural that the numbers have evened out a bit more, but there are still plenty of DKs and they seem to be doing just fine tanking Icecrown. We'll see if things look different when the hard modes unlock and if DKs (of appropriate gear and skill) struggle on those fights, we'll buff them.
We don't balance around representation. We do take notice when populations suddenly shift, but that hasn't happened in this case.
Mage
Best talent spec for raids (Source)
Some of you Fire mages are having too much fun ranting in this thread instead of focusing on what I was actually saying. :)
Is Arcane generally above Fire? Yes. The difference may only be 10% though, and Fire is still above many damage specs. Is Arcane so much higher than Fire than Marks is to Survival? Not really. Yet we see more Survival hunters (in this particular data set on one boss) than we do Fire mages. Clearly more is going on that players just gravitating towards whichever spec does the most damage. (The key word is "just." Players definitely like specs that deliver the most damage, but that does not appear to be the sole governing concern in this case.)
There are a lot of things contributing to Arcane beating other mages. Incanter's Absorption is probably way too good in conjunction with kind Disc priests. Arcane benefits a lot on movement fights like PP. Arcane benefits a lot from using those Innervates that the Fire mage can't really use and the healers (for the moment at least) don't really need. As Lhivera points out, Frost can do decent (not stellar) given the chance, but fights like Marrowgar really exploit (in a bad way) Frost's relative lack of pushback resistance.
We'd like to get the mages closer together, and that's something we're still going to work on. ("Wait until Cataclysm" is something snarky players like to say more than we do.) What we don't want to do is suddenly catapult Frost up ahead of Arcane such that every mage feels like they have to change... again. Close, without going over, is kind of the mantra at this stage. :)