Even if the game doesn't have a file sharing system built into the game which at this point looks like it won't , there will be other ways to download rosters. Somebody in another thread even posted how it could be done on both the PS3 or 360. And there are ways to get around some of the 360's restrictions in terms game saves having to be tied to a certain profile. For the PS3 it should just be as simple as using a USB since those restrictions don't exist. The only way these wouldn't work is if there was some restriction actually built directly into the game which I highly doubt would happen. They may not make it as easy and covenant as it could be by having a file share system built into the game, but that doesn't mean they don't want or would restrict sharing through other methods.
So I am not really worried about being able to get other people's roster/files because there are other methods/ways to do that. What I worry about is will the player editing and creation be too limited to actually replicate certain NFL players in terms of their abilities and tendencies. The indications so far is that individual player customization may be very limited compared to how deep the other customization options are.