You are actually right and down voters have no clue (and this is what I hate about HN, if you don't comment then don't downvoye)
To answer your question though - Microsoft has a lot of git extensions that they are slowly submitting upstream. Hence git is usable for their megarepo.
Look up GVFS on GitHub, very cool work.
Same for Twitter (they are not submitting upstream though as far as I know)
What do you think? I reddit.