Yer but the thing is that I love him as the Doctor same with the person who plays Jack in Torchwood. I will always think of them as the Doctor and Jack from Doctor Who. Its hard to think of them in somthing else. I don't think David Tennent could pull Moist off well.
"You know why big brothers where born first? It was so they could protect the little brothers and sisters who come after them." Ichigo, Bleach Episode 3.
Were he still alive, I would gone for Jeremy Brett (the best Sherlock Holmes) but as it is, I think Alan Rickman would be perfect in the role of Vetinari.