Delayed to make the "best gaming experience possible."
"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."
Hope noted that they're eager to get Steam Machines out there, but their number one priority is making sure they create the "best gaming experience possible."
How this will exactly impact the release of the SteamOS or all of the Steam Machines various PC makers are working on is unclear at this time.