Facebook initially had many important distinctions from Myspace--exclusivity, better privacy control, and no potential for flashing neon design abortions. The first two are gone now, so I think you're pretty much right.
I do wonder if it will be replaced by another actual social network or if social networking features will be turned into a basic protocol that can be shared and distributed from any number of unrelated non-commercial servers or services.
It was exactly this that made Facebook great for college kids and drove its initial growth. Facebook was once a quasi-private space, and that was all kinds of fun. Sort of a unique online social experience (and not in the buzzword sense of "social") that was available for a couple years.
I do wonder if it will be replaced by another actual social network or if social networking features will be turned into a basic protocol that can be shared and distributed from any number of unrelated non-commercial servers or services.