Blizzard and Valve have both successfully integrated OSX builds into their pipelines. That's two developers of AAA titles at least, and there's plenty of great indie stuff available like Minecraft.
You do know that DirectX rules the gaming world right? Having 2 developers on mac won't change the fact that all games run faster/better on windows first. Games of the year like Mass Effect 2 (or many other top selling PC titles) were not released on mac.