In this respect, I think github's killer feature over sourceforge is its focus on people instead of projects. Perhaps we could call it an increased democratization of open source.

Sourceforge is centered around projects. You have to register and get approval for each project separately (at least you did a few years ago, it has been a long time since I last went through the exercise). This left a significant percentage of projects with descriptions of the author's intent, but no actual code. It also meant that any third party contributions had to go back through the author (who might have lost interest).

I have never seen a project on github with no code. There is no approval process. You simply push and you are up and running. Forking allows others to start contributing right away without any action from the original author (and github really encourages you to fork projects). Then the tools that github provides makes collaboration way easier than it was in the past (pull requests vs emailing patches).

I agree with all of the things the author notes, but I really think this is github's killer feature. (Hope I didn't come off as too much of a github fanboy).