Is NBC getting The Jay Leno Show out of the 10pm timeslot now to placate its affiliates and prevent them from tieing up (or torpedoing) the Comcast acquisition? Could the move even have been at the explicit direction of Comcast to protect the deal?
That's by far the most persuasive reason I've read about why this may happen, and particularly why now.
Otherwise making a move now, instead of next fall, makes no sense. Whatever reasons you can come up with for taking Leno off the schedule at 10pm, make more sense in August, except near term affiliate placation. The affiliates could have made a lot of trouble between now and next fall in the NBCU-Comcast deal approval process. Now, presumably they'll quiet down.
However, in the long run, can this do anything but anger the new Comcast overlords against the affiliates? Whatever problems they may have with the local affiliate broadcast business model certainly isn't helped by this episode.