This is the big issue with using hg anywhere I've worked. Not even that people are experienced with it -- just the name recognition usually wins out.

Honestly, I also think github's defacto status is a major obstacle to adoption.

There are actually projects that let you work with an hg/git repo and push to the other type. http://hg-git.github.io/ for instance. No idea if these things are production ready or not though.