From a post on the first page of the website:
Class changes deployment frequency during Beta Test
Seriously though, it's easier for to focus on only a couple of classes at a time. We find that way we are more in sync on the direction of the class and its problems. We don't work in an environment where each person goes to their desk, throws in the talents for one class, and then we pour them all into the game. A lot of the time it's 10% actual talent implementation and 90% brainstorming and discussion.
Mages recently got a fair amount of attention and death knights always do, just because they have the most catching up to do to the years of analysis and design that's been done on the other classes.
But even then, you're more likely to see ability changes than number adjusting. We need to feel like the abilities have a chance of working out before we go into the mode of comparing everyone's dps and threat and survival in a variety of situations. The encounter design and item design need to be at that level too. We're still debating things like encounters and raid stacking will work. Think about all the changes: many stats are universal now (meaning melee hit and spell hit are the same as far as items are concerned), most buffs affect the entire raid, we're trying to offer fewer very specialized items as random drops, etc. etc. It ends up being a lot of changes all with ramifications for every class. (Source)
QQ less and pay attention more, please.