Well, it's not just "git"... it's any of the tools people use to compare and collaborate on text files. Throw it in a Rietveld instance or Gerrit, and you can review changes and make comments like with any other code review. If you prefer just throwing it into kdiff3 or something, you can do that, too. If you like Word's "Track Changes", LyX has that (though that means everyone has to use LyX as their editor).
The point is that a simple text-based source format opens up the possibility for lots of different collaboration models that the Word software monoculture prevents.
The point is that a simple text-based source format opens up the possibility for lots of different collaboration models that the Word software monoculture prevents.