Your cynicism is well founded, but until that happens, enjoy the platform.
If they keep making them, I'll go with it.
I don't think that they're making identical mistakes, but we can't assume that it will last.
Obviously it’d be nice if it was the first social network not to either implode (Livejournal, Tumblr, Twitter), or fade into irrelevance (Friendster, Bebo, MySpace, Digg), or just ossify into mind-numbing tedium (Facebook, LinkedIn), but, well, if it does, presumably there’ll be another one along at some point.
(I realise that you could probably argue Digg either way, here. Digg had a multi-paradigm end.)