The Doctors always go too soon. I guess it's a consequence of the size of the show now, the schedule that seems to have them working 10 months of the year and the increased attention the actors get.
Fake Edit: I went into writing this post about to talk about how the original run's Doctors lasted much longer, but having looked it up it seems the longest was Tom Baker's run from 1974-81, all the others seem to be around the 3-4 year mark, so actually they're not going any more quickly than the others, Tennant and Smith have actually put in more time than most of the others. I'm not sure why I assumed they'd left earlier. Chalk it up to what I was saying about not wanting them to leave the role I guess, we've been lucky that all three Doctors in this run have been great so far. Just makes it even harder to let go and look forward to another I suppose. There's always the fear the next one will ruin everything.
I think it'll be especially hard for American audiences, where there are many who may not have watched the show before Smith. I wonder how this will affect the show's growing fandom there. Hopefully the show will continue to do well, we all have to have our first regeneration sometime, I suppose!
