The project is based on git-annex, which is an extension that treats big binary files differently. Namely, it doesn't check in the file contents, so you don't get full-file versioning. You can find out more at http://git-annex.branchable.com/.
Technically you can use the SHA backend to git-annex, so the actual file contents can be tracked by git, giving you "full file versioning". It's just not checked into git.
Additionally there is a bup backend target for git-annex. Bup is targetted as a rsync-like backup service that can do incremental backups and ought work OK with large binary files.
https://github.com/apenwarr/bup/
It was through Bup that I originally discovered git-annex.
