It's true that most e-pubs do have some clause about promotion in their contract, though the ones I've seen just require the author to promote their work "to the best of their ability," which is pretty unenforceable.
While it's good to have a blog or website for those who want to follow you, I have to question how much difference an author's promotional efforts make, overall. It seems to me like promoting your work unsolicited on the internet is the equivalent of sticking flyers in the doors of random people. There are just so many people out their trying to sell their stuff, it comes across as spam more often than not. (Though if anyone has information that contradicts this, I'd be interested in hearing.)
As others have said, a publisher's reputation is what sells e-books.