See....right there, I think you are overstating the Kinect/Move and the value. I mean, technically thats true. Lets say the "fullest ability" was measured in terms of distance......lets say 100 yards. I'm paying 400 bucks for 95 yards. So far Kinect and Move have proven to be the other 5 yards. I just feel users should be able to make the choice on whether they want it at it's "full potential" or to use your words "full ability". I could go buy Street Fighter. Some people would argue that if I don't buy a fight stick, I'm not able to unlock the full potential of Street Fighter. That's argument for another day, but the point is, I have the option. I'm sure there are some SF bundles out there that come with one of the fight sticks, but regardless of how much some people may think it adds to the game, it's still an option for the consumer to make that decision.
Now, if the Kinect drops and its as yall say and devs all of a sudden start making these amazing Kinect games, I'll gladly eat my words. You are correct, a Kinect for 100 bucks over the life of the system is not a steep price. But it still should be up to the consumer because at this point it's still just an addon. Take away voice commands, take away auto sign in on the Xbox One and the people using it will get along just fine.