It's a bold assumption that those open source projects are larger than facebook, a company which employs 2000+ engineers.

webkit and chromium have about 6 or 7 million lines of code and < 200,000 commits.

Facebook 6 months ago had 62 million lines of code and > 1000 commits a day.

http://www.quora.com/Facebook-Engineering/How-many-lines-of-...

Also, there's a difference between those open source projects using large repos with git and Facebook wanting to increase developer efficiency. Developers sitting around waiting for a rebase doesn't really pay off, where as an open source project can get away with it.

You really believe that Facebook couldn't find a competent C programmer to make some changes to git?

Would you accept an answer that complains about how hard it is to hire programmers? :)

Its still one of the coolest and best paid companies out there! You really think they couldn't hire a few guys from core git team saying - "Dude, just improve git and we'll pay you?". You must be kidding

WebKit uses Subversion (http://www.webkit.org/building/checkout.html). You can use Git with the WebKit repo, but it's git-svn doing the work...

The idea is that you should not have to modify git or mercurial. Instead of modifying git or mercurial to handle a single repo for your entire company, you should create a system that uses them to handle many repos in your company. You don't need C programmers to do this with git.