I (and I suspect many others) use github because it's a git that just works with no fuss. *That* it does and does well. It's "forking" feature is nice, but nothing I couldn't just do by cloning someone else tree. Sourceforge did many of the things you state and it still got so far. Github embodies the current open development paradigm. If past is prelude, though, these things tend to expire at some point.