I'm not sure git is an example of capital-G Genius, since Linus had been using BitKeeper, a commercial distributed revision control system, for about five years by the time he wrote git.
More importantly, Linus took a good look at Monotone, with which git has a lot more in common than with BitKeeper...
and the same is true of Matt Mackall/Mercurial of course.
The incremental improvements in git/Mercurial were of course significant in getting wide adoption.
