Good point about Potter, and about the Eddington movie being on HBO. But, wasn't Potter before Doctor Who? If that's the case, then you'd have to count the Hollywood productions Eccles was in before Who, as well. And while HBO is a premium pay cable, NBC broadcasts Heroes freely (as far as I know). Still, then you run into the argument of how paying for HBO and paying for your tv license in the UK compares.
Not really trying to make a major debate here, or anything. But, I'm of the opinion that I don't believe Tennant is in any more lucrative position than Eccles during/post Who era. He just happens to be currently popular with the UK crowd...