@sdornan: Listen, I understand that if a game is requiring you to jump in the air or dance a certain way, you can't sit on the couch and do it. But this whole question of "can you even make a game that lets you sit down" isn't just a completely common sense one to answer, they've demonstrated that this is the case multiple times already. None of the games they showed at E3 had people sitting. So?
No, you can't jump in the air without actually jumping in the air. This was a big deal or a worry? It's like worrying that Rock Band 3 won't let you play the drums with your regular gamepad.
Was this ever actually a question or concern? If it can detect the motion of your hands, fingers, and the rest of your body, why can't it detect if you're sitting down? Or, why couldn't it detect those things WHILE you're sitting down?