I said I was more excited about the Steam console, not that I would buy one instead should MS lock down the 720. I'm excited because Valve has traditionally made some truly excellent games. If they can translate that excellence into the hardware arena then we could see something interesting and new.
The 720 is a generational upgrade, but is not, strictly speaking, new. The Valve console, on the other hand, is from someone whom I have developed a good deal of respect for over the years. I'm curious to see what they come up with.