Steam announced what could be a big deal in the console market – SteamOS: an open source OS for dedicated living room consoles. This is a big deal because Steam has been a big deal amongst PC (Win and Mac) gamers. Bringing that to the living room in a compelling way might be a disruptive attack on current consoles.
An AppleTV with an App Store would probably blow right past this and all existing consoles because of the Wii-factor: selling a gaming machine to non-gamers which is a much, much bigger market. AppleTV would garner a huge margin of the casual/indie games with big titles thrown in (just like and hand in hand with iOS). AppleTV also would benefit from being an everything box because it wouldn’t be solely gaming.
But considering the AppleTV AppStore and gaming focus is just a nerd-dream currently, this is potentially big news. The pivotal variable to watch here is what hardware support it gets.