Valve confirms Steam Machine will be priced ‘like a PC with the same level of performance’
(www.videogameschronicle.com)
I certainly don't see it, but I guess they are confident enough that there's a market for people who want access to the gigantic Steam library but also don't want to build their own PCs? Maybe it's going to run very smoothly, but that would also be dependent on the optimization of each individual game.