I'm sure they can put a case together to reassure developers looking into Kinect games that this move will increase the Kinect install base rather than decrease it.
For developers that are Kinect-focused to the point that it is obligatory, that might work.
For developers that don't rely on this and have the option to go without, the market penetration of Kinect is going to become important.
If the ratio skews heavily against Kinect, then they're going to evaluate whether an larger Kinect base in absolute terms is worth catering to versus a larger fraction of Kinect-free setups.