It might be possible that Bethesda talked Microsoft down from pushing Kinect into Skyrim at launch by agreeing to making the first two DLCs Xbox exclusive for a period of time.
Obviously there's holes with this idea, and there's no way, short of Todd himself revealing it, to tell if this was the case, but an idea, nonetheless.
As a side note, I'm hoping that Beth take a nice long time to make their next DLC smooth and creamy for all three platforms. Maybe get Dawnguard out on PS3, too.