I don't know. There are a LOT of people that use wine for things other than gaming (though that seems to be its greater use). Plus there's the immense number of older games that aren't and won't be available through Steam, that use DirectX 9 and 10, other applications (modeling software, visualization software, etc) that also rely on DirectX technology to function properly, etc. Wine could actually GROW once and for all and stop playing catch up with the games, and instead focusing in more important parts (like proper GDI+ implementation, Aero implementation [for when an application requires it, and map that to AIGLX and Compiz, for instance], and many many more compatibility fixes, etc.).
Originally Posted by deanjo
Steam on Linux (with a nice share of games) would also mean one crucial thing: Linux is a viable alternative to Windows, and may even benefit more console porting than Windows. OpenGL development for the games would instantly mean virtually insignificant effort to port to Mac, small effort to port to Wii and PS3, and even Windows ports. Microsoft-centric development, even if the platform supports OpenGL, has been focused on DirectX, which only translates into Xbox portability. OpenGL actually opens up a broader audience, and can even cater the most widely used OS in the market: Windows, which needless to say, if I were a gaming company manager, would be a no brainer to migrate development and training. The investments made to migrate the underlying API of the games, most likely will be made up for if it is available on more platforms than two.