From my perspective, the main Dropbox feature that all the "thin layer on top of VCS" clones miss is the conflict-resolution behavior of Dropbox. If both you and someone else edit a file called "stuff.txt" at the same time, you'll end up with two files: "stuff.txt" and "stuff.txt (other guy's version)". Neither person's changes are blown away, there's never any merge conflicts, and the history remains linear.
I'll have to see if Gitdocs does anything like that.