I think you touch on an interesting issue. If I look at myself and my life, or at my friends and acquaintances and their lives, there seems to some inherent transience and change in my and their social world. This change can be prompted by entering new stages of life, or moving from one place to another, or simply a result of a changing environment. But it's there. I think for a large amount of people, maybe the majority, social life always changes over time.
This, of course, can pose (and has posed) a problem for companies that have 'social' as their core mechanism. Where companies like Apple can rely to a certain degree on the continuity of lifestyle of an Apple customer (well-off, relatively, for one), 'social companies' have to deal with a constantly shifting landscape.
If such a company aims at a particular demographic, they face the problem that merely being popular among another demographic (previous generation) is a big reason for them to be 'uncool' (snapchat/facebook).
I don't know if there are companies that instead focus on a particular generation, but perhaps that'd be an interesting business model. Grow with your customers.