The point of bringing up Office was to provide an example of why a person might need Windows, not to highlight it in particular. Your argument was that people wouldn't desire SteamOS if they wanted to do other things. Why wouldn't they go with Windows 7 with Steam, rather than have two PCs?
Well, as I see it, they only need Windows for business applications. The consumer gains literally nothing from Windows in and of itself: Windows remains dominant because people use it and design for it because Windows is dominant. Everything but business software and games, and the software to design those two things, has been done better or as good under different operating systems.
So, if a gamer doesn't care about running business software, why wouldn't he go with a pimped out gaming rig from Steam, running a custom OS designed around playing games? Assuming it can run Windows games and the entire Steam catalogue, what reason is there for caring about Windows? They'll still be able to do everything else they usually do... check email, read the news, jerk off to porn.
And like I said, most gamers have two computers. Keep Windows on one, and buy a Steambox.
Also, there are a number of reasons for disliking Windows that don't revolve around being a Mac or Linux fanboy. It really isn't a great OS. Hasn't been in a really long time.