Yes, you are probably right! I hear Tennant can be a bit devious when he wants to be. Could he have arranged for Russel Brand to meet Andrew Sachs' granddaughter? Could he have slipped something into their drinks to make them a bit more amorous? Could he have hypnotised Brand into calling Andrew Sachs about it? I think he could!
Seriously though, damn shame. I'd really have liked for him to do another full season under the Vast Toffee (MN) - it's got to be better than being under RTD!
A Christmas regeneration next year? Or will that Christmas special (assuming there is one, of course) be the new Doctor's Christmas Invasion? Probably filmed as part of the 2010 season, so most likely.
Sad to see him go. A very tough act to follow, Mr. Joseph (or whoever!)