Except that if the Django core developers thought that using Git, mercurial, or github would grossly improve their workflow, don't you think they'd use it?

They may be perfectly comfortable with their current tools - we agree though, this is not a source control issue. It's is a personnel, and social issue. DVCSes are not magical, and github isn't a cure-all.

If the problem is with the people; we have to fix the people, get new ones - not change the tools.