Why would Windows users want to put up with that anymore than we do? What makes you think they would like all the trouble involved with that when we don't?The best operating system for playing games is the one that lets you keep your word processor, instant messenger, email, and music player open in the background while you play. The worst is the one that will force you to shut all that down just to screw around for a few minutes.
This was tried when Apple went X86. The Cedega guys whipped up a product called Cider that was only available to game publishers to bring games to OS X via Wine, it did not work out well. Even with all the recent progress with Wine it's still a terrible kludge.
You are delusional if you think valve ported steam to linux for ANY reason other than their upcoming steambox initiative.