
Those are the only two instances I can think of in which an online connection is absolutely vital. Everything else--streaming, social connectivity, achievements, etc.--are just unnecessary garnish IMO. Nice to have, but not vital to every gaming experience by a long shot.
The only other logical explanation is DRM. In fact, THIS is probably why they won't be charging the rumored fee on second hand copies--it'll probably just stop the game from playing after 24 consecutive hours or something. *sigh*