Citing developmental delays with the Steam Controller, which has now gone wireless, Valve has moved their estimates of when the first Steam Machines will launch to 2015:
We’re now using wireless prototype controllers to conduct live playtests, with everyone from industry professionals to die-hard gamers to casual gamers. It’s generating a ton of useful feedback, and it means we’ll be able to make the controller a lot better. Of course, it’s also keeping us pretty busy making all those improvements. Realistically, we’re now looking at a release window of 2015, not 2014.