Many, many games do require DLC to stay profitable, although I'm not convinced one way or another that the EA sports titles do (maybe they do maybe they don't, I don't have the proper info to say one way or another), as they are wildly popular games.
But it seems to me they are using a DLC price-tag to justify adding some features that the hardcore set are asking for without actually taking away from standard development. Clearly I have nothing to back this up, its just speculation and I'm not posting this as fact, but there is nothing that says they had to create AFL uniforms for Madden or these new web features for online dynasties, and its likely (especially with the previously mentioned ongoing costs with web content) that if they didn't have the idea to charge for them they just wouldn't have done them. These are features that really aren't selling any extra copies.