> They don't (want to) understand that social network means that users talk to each other.
No, I think they perfectly understand that. The iPhone is their social network. You can use it to manage your contacts, call, send messages(both long and short), share photos and videos, and video chat. What more else do they need that they don't already have?
MobileMe included user-to-user communication (iChat), as well as a Gallery that could host publicly-accessible pictures. If you squint a bit, those were social network features. Unfortunately, MobileMe bombed pretty badly - and very publicly.
