Even if this is true, it would be mostly irrelevant for purposes of game performance.
Well it depends whether or not that performance is later made available. If there is a reservation of say 15% of the performance for Kinect and Microsoft chooses to allow all of it to be used at a later date then there would effectively be another 15% of performance available.
Well it does in so far as Kinect 2.0 would now be 'free' as opposed to the x% of system power we were all mentally reserving for it instead.
There is also this point as well.