Check the franchise draft classes. Plenty of high potential players go in the late rounds of the draft. Some that are immediately good, and some that take a few years to get there.
"Tom Brady" "Terrell Davis" and "Deacon Jones" would and do happen in Madden 2010. As does "Tony Romo" but previous Maddens never progressed a player who didn't put up numbers. Madden 2010 does.