As a Ruby/JavaScript developer I find it very bizarre that you don't know anyone that has used git professionally. Pretty much everyone I know uses it professionally and I'm a bit taken aback when someone hasn't even tried it.
But people in games probably wouldn't use git anyway on account of its poor handling of binary files, and limited scalability in the face of gigabytes of stuff. (I have a suspicion it might be a bit difficult to explain to many/most artists anyway. And a fair proportion of programmers too...)
Of course, this shows nothing more than that we both live in our respective little bubbles ;) But my impression, as a bit of an outsider, is that the HN hivemind is made up of the same people that frequent GitHub. That is, mainly (but of course, not exclusively) people who work with web-python-ruby-javascript-etc. - thus naturally magnifying the apparent importance of GitHub. But I suspect the HN population is not representative, and therefore GitHub's popularity amongst the HN readership probably does not extend to the programming population at large. And this is certainly backed up by my experience.
(All standard disclaimers apply.)