In most previous console generations consoles began with clearly superior graphics quality to PC's of the time. The Xbox360 and PS3 changed this trend by being barely ahead at all, and the latest generation of consoles is apparently behind right out of the gate [1]! Consoles offer inferior graphics performance and inferior input (you can always hook a gamepad up to a PC!), but they're relatively cheap and have pretty effective DRM.
This situation presents a big opportunity for Steam. Make steamboxes as cheap and simple to use as a console and you effectively have a console! If you do this while providing superior image quality and supporting better forms of user input, you have a contender. Unfortunately, Valve isn't going to get much help from game producers right away. They'll prioritize whatever market generates the most profit. Steam is going to have to make steamboxes popular before game studios will prioritize the Steam experience vs. that on other consoles.
[1] http://www.eurogamer.net/articles/digitalfoundry-battlefield...