probably the closest thing you can get for "console-PC"
http://www.dell.com/us/p/alienware-x51/pd
even then it still more expensive than console and missing component like keyboard and mouse (I ignore monitor since is like saying you need TV to play PS3)
anyway about steambox. probably just like PC in the link. it over simplicity of plug in and play. thought i am bit worried that it use linux since majority of steam will not work