Hmm. I wasn't thinking about it from that perspective. Still, I don't see github as a replacement, but simply an optional nice UI for git collaboration. It's easy to set yourself up so that if Github went down or you wanted to move off it, you could. The only tricky part would be not investing too deeply in the issue tracker, but that's not a replacement for git anyway.

I'm not sure they can be said to be incentivized to do something that's nearly impossible.