Personally I have no idea, on this discussion board it's all basically peanut gallery economic theory. Though while it seems to come up often as a fallacy in hockey discussion, this is an area where I assume an appeal to authority works. Sony isn't going to not want to make more money, and they're going to employ teams of people educated in finance, economics, marketing, etc, to figure out the best way to make the company the most money. Sometimes this doesn't work as it could just be a stubborn CEO calling the shots on it, but I'd be fairly certain people at Sony would have looked into the idea of putting their exclusives on Steam crunched the numbers and decided it wasn't in their best interest to do so.
One angle to look at it is if a person doesn't have to own a PS to play God of War because they can just get it on PC then they also don't need it for Assassins Creed or Call of Duty or whatever and Sony loses royalties on those cross platform sales. Microsoft decided they could make it work putting Xbox games on PC, but again those are games that will still be played on MS Windows and that's a piece of the equation that Sony or Nintendo doesn't have.
