I didn't, the Hg dev simply used Facebook as a very large, well known software shop that uses Mercurial. We could swap out "Facebook" for "Mozilla" or "Nginx Inc." or a number of open source (either community or corporate backed) projects.
We could do the same thing with Git though, so clearly source control scheme is not strongly correlated with actual success of the project -- which makes sense.
The point was that there are a lot of git "wrappers" created to solve the problem of Git's usability. The same doesn't happen with Mercurial, and it isn't just because of a lack of use, as demonstrated by X, Y, Z prominent/large software companies/projects using it.
