But what if Feral Druids only make up a small percentage of the tanks in Ulduar? Should Blizzard nerf the 5% of tanks that are Druids down until they're only 2% of the population? Just because classes are overpowered doesn't mean that actual class populations are, and all of these things go into the mix when Blizzard makes decisions about how to balance the classes.
Look at Hunters as well -- just last week we talked about how the class population is falling off, and yet they're one of the top three classes played on both factions. So should Blizzard buff or nerf them?
If they buff, more people will play Hunters, but that might lead to an even more imbalanced representation. And if they nerf (to bring them down in line with other classes), dedicated Hunters, whose numbers are already dwindling, will feel cheated. Arena representation is another place where this dilemma is clearly seen: Blizzard isn't just balancing class abilities, they're balancing out class popularity as well.
GC makes another good point when he compares what the Starcraft team is doing with balance right now: in RTS games, you don't see as much "preference" going into the decision to play -- if Zerg are OP, you play as Zerg. But in MMOs like WoW, player background and choice plays just as big a part as endgame abilities and talents: if you feel like you want to be a Priest, you'll play them no matter how underpowered they are.
Very interesting stuff -- Ghostcrawler definitely gives an interesting look into all of the different torches Blizzard is trying to juggle when they make changes. He also says that many guilds, especially high level guilds, are more attached to the classes they play (because it's what they know), and that they're more likely to just up their own game rather than switching in and out classes based on whatever's been nerfed or buffed lately. Play style, class balance, and popularity and class loyalty all go into the equation when it comes time to put a class up on the operation table.