Here's a fascinating post over on Terra Nova. Joshua Fairfield has been playing a lot of Arena PvP, and he suspects something very interesting: that the developers might not be trying for equilibrium in PvP at all. They may actually be trying for imbalance.
Our assumption, he says, is that with every nerf and/or buff, the developers are trying to reach a nirvana of balance-- a game where every class has an equal chance to win when all of their abilities are used correctly. Keep in mind that the "chance to win" could only involve a percentage of the time-- Blizzard has already stated that they're working for a "rock, paper, scissors" solution, where rogues beat casters but warriors beat rogues, and so on. But we've assumed that the main goal is a balance, where as long as every class is played well, every class will win a certain percentage of the time.
But Fairfield suggests the opposite-- that "games that seek permanent engagement by communities," i.e. MMORPGs like WoW, are actually working against equilibrium, and fighting to keep things constantly interesting. Mages are winning because of Pyroblast's high damage? Nerf it to make Mages use other spells. Warriors are being kited around? Give them a way out of it, so other classes have to learn new strategies.
That's a wacky way of looking at game design, but it works for games like WoW because we're already expecting the rules to constantly change. Chess has an established balance-- rook moves a certain way, queen moves another way, and every game they will always move those ways. But WoW is dependent on the rules changing every patch-- if players maxed out their characters and learned all possible strategies, they'd quit paying the monthly fee. So in that strange sense, Blizzard should be happy when lots of players cry foul over a nerf-- the more players they affect with a change, the more they can keep interested. "Any change disrupts the current equilibrium," and forces players to figure out new ways to win.