Not all games are going to utilize Kinect features. What have we seen so far that's "Better with Kinect"? Not much. No reason for me to plug mine in at any rate and I bought two sensors (for use with the PC).
The vast majority of third party games in particular, barring Kinect specific games, won't bother with Kinect by default. At best we might see it used for voice commands, which wasn't exactly a game changer for Mass Effect.
So why won't they bother with Kinect features? Because third party developers will be publishing the same games on other platforms that don't use Kinect. PC and of course the PS4. If they really want to leave camera based input or mic based input features in their games, then they'll just require additional hardware for said platforms.
The only real advantage of Kinect as a default input is for the UI itself, which will be engineered around it, similar to the way Win8 was engineered to work with touch screens (which was perhaps not the best call since everyone did not go out and buy touch screens and Win8 tablets).
Don't get me wrong; Kinect 2 was the key standout feature that I said would interest me in an Xbox 3 before the reveal. I still have fair expectations for it since I've seen plenty of interesting things done with Kinect on PC, but until that potential is legitimately used, then it's just an alternate UI and a creepy always on camera/mic when I'm playing something that doesn't need it. I'll probably make a little sound insulated box that covers the cam when I pick up an XB1.







