Maybe so, but it's a cumulative effect which can end up snowballing.
Who'd have thought Valve would port Steam and a bunch of games to OSX even just a year ago, especially after Newell's remarks about Apple's lack of enthusiasm? Now, along with Blizzard and id, all three of the really big PC devs are making native OSX games, there's less reason for a few million Mac gamers to buy Windows licenses and a good spur for other developers. It seems likely that Valve will do the same for Linux, so there goes another portion of former Windows gamers, and the start of a new self-sustaining ecosystem.
Nature abhors a vacuum and Microsoft's wilfull and rather stupidly shortsighted neglect of PC gaming has created exactly that. The days of Age of Empires, Freelancer, Mechwarrior and Flight Simulator are long gone, along with Bioware to EA and GfWL's a total turd.
There's plenty of money to be made by canny developers even in the relatively niche OSX and Linux markets and growth there will encourage others to jump on board. It won't bring Microsoft to their knees, but I can't help feeling a parallel with the browser market where Microsoft's hubris and lack of development of IE led to FireFox first gaining a foothold, then taking off and taking huge chunks out of them, followed by others- such as Chrome- weighing in and gaining traction as well. Their obsession with keeping Sony out of the living room could prove to be their biggest folly yet.
