I'd say this is frequently the case for the people still holding out on mercurial. I know I've repetitively had a good degree of cognitive burden trying to submit things in a git/github fashion to the FOSS projects using hg - my mind is fixated to the git flow and this flow breaks or has encumbrances for competitors such as bzr and hg ... as far as I can tell those tools are more restrictive and harder to work with to do things that are a breeze in git.
I'd say there's many more people coming from git tools these days, researchers and lab users included, in addition to the Whitehouse being users . Have a look here:
https://government.github.com/community/ , see also
https://github.com/whitehouse . I see folks from NOAA on the numpy/scipy ML having repos hosted there too... I only see people in industry using mercurial when they need a free account with 5 team members.. This is just github - actual usage of git is much higher with atlassian even addressing it very seriously in their tools - atlassian normally being the strongest enabler or focal point of mercurial usage I've seen.. So it is my very strong believe that you are indeed making it harder for developers to contribute by having the additional burden of SCMs they are not familiar with.