Well, it's unsportmanlike conduct when nobody is around, but you still see guys doing it when being tackled from behind, just not that a gaudy, show-off sort of way.
To answer the original question, though, it seems that the game has removed instances of unsportsmanlike conduct on purpose. In the new (360 and PS3) version, they seem to have just never added these things in, but even in the old version (PS2) it was taken out several years ago. Perhaps the NCAA put pressure on EA to remove blatant unsportsmanship, similar to how the fans charging the field was removed.