Damn, another project giving up on Mercurial and switching to Git. :-/ A few more major ones and basically nobody is using Mercurial anymore. How sad.
Still, it's great we've had all this DVCS craze in the past years, we ended up with great open source tools that improved a lot over the CVS/SVN of yore.
Mercurial was more friendly to us Windows developers.
But with Microsoft embracing Git this isn't any longer the case.
(Maybe the way to advance the poor Gui user interaction experience is to write frontends for it?)
Addressing your actual point, most shops won't use the full value of a dvcs, but they'll all get some benefit of it being a dvcs because each and every developer's machine has a backup of the central repo which, in the event the main git server dies, can be used to restore everything to it's previously happy state. When you use a vcs like svn, you need to be a lot more paranoid about backing up the central server or you risk losing revision history.
They also offer a powerful diff/merge tool with language-specific support. http://www.semanticmerge.com/
In Mercurial I never lost a commit, even as a beginner. In git I managed to accidentally make commits unreachable (yes, I know how to recover, but still, it tooks a bit of googling and trying).
I very rarely need git's "remotes" feature. There's rarely a need for me to know where someone else's master is at the moment. I understand why git is doing this and I get that it's pretty flexible, but most of the time Mercurial's simple branching model is enough for me (I don't like bookmarks, they confuse the hell out of me).
Also, my repositories are usually small enough that I don't notice the Python overhead compared to Git. My ultra slow old disk is more of a problem in that case.
Mercurial's help is MUCH better than git's. Git's manpages are so famous for being mostly useless that people even write joke tools that generate gibberish manpages. Mercurial has a very clean documentation, with `hg help ...` just showing you what you need to know instead of (on Windows) using your browser to render an HTML manpage.
And lastly: Will git 2.0 ever come out for Windows? Seems like nobody is working on that, so we Windows users still get some preview version 1.9.4 at the moment. That doesn't look to me as if Windows was a first-class citizen in git.
Fun fact: Converting from git to mercurial is the easiest thing in the world (`hg convert my-git-repo new-hg-repo`), but the other way around is weird and complicated to setup (talking about hg-git).