Google TV, Nexus Q etc are trying to crack a different nut, and one of the hardest ones out there. The fact that these things are called set-top-boxes in an era where TV's aren't big enough to put anything on top of them is an indicator how long people have been trying to make it work.

XBMC has been most successful because They have focused on providing people what they want. Every company has delivered something that they would like people to have (and ideally pay them lots for content).

Consoles on the other hand seem to be marketed by Black magic, Hype, and dodgy stats. That does seem to be more Microsoft's game than Google's, but they are gaining ground.

I figured they are making a combined TV and game device. Heck some Rokus come with Angry Birds and games for purchase, so it wouldn't be the first time.