Some people have mentioned that Lee is a better blocker than Finley, but I'm not so sure about that anymore. I've read good things about Finley's blocking in practice, and he made a good block on Ryan Grant's TD run against the Bills. Although both TE's will plenty of snaps this season, I see no reason not to start Finley. It is obvious that he is already a far better receiver than Lee, with way more upside, and as far as I can tell, they are not far apart in blocking skills.
I think coaches send a bad message to the team when they do not reward superior play with more playing time. I remember at the beginning of training camp, one of the coaches, I think it was Philbin, was asked if Finley would have a chance to beat out Lee for the starting TE spot, and he said something like "Absolutely." So the coaches are open to the idea. When you take that into consideration, what more could Finley possibly have done to beat out Lee? It's not a knock on Lee, as he has looked good too. Finley is just better, so he should start.