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.