Agreed, Valve won't be officially supporting Wine or Crossover in SteamOS and they shouldn't because then users will expect perfect compatability with *ALL* Windows games, which Wine cannot provide and give users with unrealistic expectations a sour impression of the platform as a whole. However, a SteamOS wiki might include an article on how an "advanced" user could install it and use "at their risk." The proper solution is to get developers to target the platform and natively port their games and maybe software (since Steam also hosts speciality productivity software). This being said, Valve shouldn't attempt to block advanced users from installing Wine if they desire to--so far they haven't.

The Wine software in Debian Wheezy's repository is old and junk but I managed to get Wine 1.7.9+Mono (latest) and the Windows Steam client installed on SteamOS. With this, hundreds of DX9-class Windows games and productivity software will run. For DirectX 11 class games, such as Bioshock Infinite, which don't yet work under the Wine layer, "game streaming" can be a solution. The official "In-Home Streaming" feature isn't available yet but you can still install Teamviewer or Splashtop to stream your games and other Windows applications from a Windows PC to a SteamOS system. It works pretty well, I've tried it on my Wi-Fi home network and it should also work outside your home network too with a fast Internet connection. However, for gaming purposes you will also need a FOSS program called Synergy to help capture and lock keyboard and mouse input inside the remoted games, otherwise the mouse input goes crazy.

Here are some shots of this in action:

http://s15.postimg.org/7xgp2394b/Steam_OSGames.png

http://s21.postimg.org/hs3faxppj/Steam_OS_Bioshock.png