Ah, that explains it. i was kind of wondering if that was the case in the back of my mind. i think it's funny cuz i just read an old interview with David and he said that he never suggests any improvements to the writers because he trusts them and who is he to judge. He obviously got over that (you can see that in the Confidential for EoT). But of course he's the biggest Whovian and quite a good writer himself, so i just think he's too humble about such things.

i didn't remember Donna stepping down, but i often read fics where people are padding about the Tardis barefoot or getting thrown to the ground during a crash landing and thinking: ouch.