Then she should use the obscure dvcs and use extensions/plugins if necessary to communicate with remote git and mercurial repos. A dev can't expect the outside world to cater to some relatively obscure choice of dvcs.

You might as well ask, "What if a developer is most productive using cvs?"

A change resulting in a short-term loss of comfort and productivity can lead to a long-term increase in productivity and equal comfort, but everyone who's used to something likes to think it's a global optimum instead of merely a local optimum. There is also benefit in using the same tools that other developers use when collaborating on a project.

Well, even among developers there's clustering. So not many developers are "most productive" using those DVCS. Probably because they have never heard of them or never used them, but it doesn't really matter right now.

If your name is Git, you're number 1 in the DVCS space. If your name is Mercurial, you're a distant 2. If your name is neither of them, only a few people have ever heard of you. Sort of like this: http://xkcd.com/435/

Ugh, I really hate how Bazaar is considered "obscure". I really think it's the most usable of the three big VCSes, and even hg could learn a bit from it. git's porcelain is an asylum escapee, it's completely insane.