That's too bad. Though I mostly use mercurial, when it's appropriate and I get to choose, I've played with fossil and it is quite a nice package. Super easy to setup, fully featured, easy to use, and does what I want. Before you shitcan the whole idea, why not play with it for a few minutes?

It would help if at least Fossil could use a Git repository (similar to the git plugin for Mercurial).

No point in having different projects using multiple version control systems.

There is when they have significantly different properties/workflows. I happen to think Darcs is supremely good for web development (probably not at facebook scale though)--it's the triviality with which you can cherry-pick patches that makes it wonderful to fast track bug fixes up to the live site while sitting on bigger, more untested changes.

I use Git when I'm releasing binaries to people (because I like its tagging better) or when I have to track some upstream code and merge in some local changes.