While I'm not a WoW player, this has been a struggle for a lot of MMOs lately. It's not terribly unusual for people to put in 20-30 hours a week, every week; and these are the ones who have school or a job; there are plenty of folks who don't have those commitments who put in way more. Balancing against that in normal play is difficult enough.

However, when it comes to limited-time holiday events, there are a significant group of players who suddenly have *more* free time since they're off work / school, and a significant group of players who have *less* time because they're spending the holidays with loved ones or at least off vacationing in the real world. You've now got a situation where anything that's even practical for the casual players with real lives is trivial for those who have all this extra time to spend.