To me it seems like Matt Smith has use his role in Dr Who to raise his profile. Its claimed he will quit after his second series which will really bolster his Hollywood career since it will give him good ratings to see if a second series will still be as popular.
Christopher Eccleston only did it for one series as he didn’t want to be type casted as you’ve only done Dr Who, well that fair enough because he didn’t shifty off to Hollywood (Remember Gone In 60 Seconds). Also he hasn’t done that much since he left Dr Who years ago.
When Smithy dies whats stopping David Tennant coming back, he did the role so well, Matt Smith is good don’t get me wrong but David Tennant and Christopher Eccleston where oh so much better.