I'm a Git guy myself, but FWIW: While Python seems to be the Mercurial project everyone remembers because it was the most recent biggie to adopt it, there's also Mozilla, and the Ex-Sun-now-Oracle projects and a couple of others.
I guess I think of Python differently from the other projects in your list because the choice of DVCS chosen by the core team seems to me to impact the DVCS that someone will choose for their library in the language. I don't really have any evidence for that, however.
Do you think that (a) language communities tend to standardize on the same version control, and if so, (b) that language communities tend to standardize on the version control of the core project for the language?
OTOH, I think the Python community is pragmatic enough that it wouldn't have chosen Mercurial over Git if it being written in Python would have been the only point in Mercurial's favor, from the POV of their requirement set. But it probably does have an emotional/affinity effect, after all language developers do obviously have to care about language! :)
Interestingly, one of the best Git libraries around is actually a pure Python implementation of Git and its protocols: Dulwich.