GitHub is a consequence not the cause (ponder for a moment why there is no MercurialHub...) It is about ability to choose best source control tool for multi-versioned distributed concurrent development. Open source devs have such choice while corporate ones - no. FB choosing Mercurial tells a lot about environment there.
Add Github to that mix and you can see why so many developers sleep like babies at night. Of course it's not rigorous, but the choice is not irrational.
It supports Git now as well, but it was only for Mercurial use when it started.
Not sure if it's still django though.
You might be thinking of http://beanstalkapp.com/ which supports svn.
> Over the past couple of months, I've been working on creating a simple but powerful hosting service for Mercurial.