I'm also not a fan of github's monoculture (or for that matter, of git's -- i rather like mercurial). I've only got one or two open-source projects out there, but I've encountered the "you are aware of github, right? why are you using <insert anything else>" mindset before.

Ideally, git or mercurial or some dvcs gains the ability to track messages and issue tracking within the repository allowing multiple frontends (such as github) to make use of a common backend model. But until then, while github is nice, I think it shouldn't be a necessary requirement for running a project, merely a sufficient one. Homogeny breeds fragility, and all.

It's likely not the only one out there though.