Well, git is a distributed VCS, so all you need in order to use it socially is the Internet. Just publish your fork on your machine (or just anywhere on the net) and anyone else connected to the Internet can pull it, github is simply superfluous for that, the Internet already connects everyone to everyone.
That's akin to saying you're part of a 'social network' by virtue of having your own homepage. Sure, everyone can come to your site to see your updates/pics/etc but it's not a fair comparison to the things Facebook/twitter/G+ provide.
No, you have a "social network" because of your social contacts, that doesn't need the Internet at all. Also, the internet consists of more than the Web - e-mail and IM are also fine tools for maintaining your social network over the Internet, for example.
Now, there may be functionality that those services provide that others currently do not, and I never disputed that. But the original argument was that somehow that little fenced garden had a large userbase.
Other than that, I am not sure I am interested in the surveillance, lock-in (potential), and manipulation possibility that FB/twitter/G+/github/whathaveyou "provide".
