I just don't share this vision. You either have -real- friends, or you have acquaintances. Facebook is not for real friends. If people are your friends and want to stay in contact with you, they will - like they did before Facebook existed.
Maybe in other villages there were other brothers who cared more about each other, and so one stayed who would rather have gone, or went who would rather have stayed. But I don't think that's a particularly positive view to take.
If facebook allows us to remain friends with more people, rather than ruthlessly pruning our friendships down to the few we can maintain purely in person, surely that's a good thing.
And that's a valuable function, and I suspect probably the reason Facebook has seen the longevity it has.
It seems very vulnerable to disruption, though. Given a self-updated directory that others can use to find you if you change contact details, and maybe given also a single sign-on mechanism that you can use with arbitrary, separate services like photo sharing and gaming, what is Facebook's USP?
Their biggest barrier to competition has for a long time been the "everyone is on Facebook" networking effect. If it's only the occasional dissenter who isn't, then organising stuff and communicating using Facebook is easier than many alternatives, whatever Facebook does to their UI/UX/privacy policy. As soon as a significant fraction of people you actually care about aren't on Facebook any more -- and significant in this context doesn't need to be anything like the majority -- that compelling advantage just evaporates.
(Yes, I'm a Facebook dissenter as an individual, and a sceptic about the long-term viability of their business in its current form as an investor.)