I have to disagree about the index, though. I use Git every day, and i'm still struck by how pointless the index and the idea of staging is.
Ditto rebase. The routine use of rebase still seems completely wrongheaded to me. Mercurial's convention of preferring merges is better, and the last few years' developments around safe evolution of history really show rebase up as the misconceived hack it is.
Mercurial got 'commit --amend' a long time ago, but even before that, it had 'rollback', which undoes the last commit, leaving the working tree untouched (that is, with the state it had in the commit), so you can make your fixes and commit again.
I'd entertain the argument that Git won because it was better if even a handful of the people who now use Git had learned both Git and Mercurial and made an informed choice between them. That simply does not appear to be the case. Git got ahead because Linus invented it, and won because of GitHub.