Git User Survey 2010 Analysis
git.wiki.kernel.org
git.wiki.kernel.org
(Either way though, they clearly do have a ton of very well-deserved mindshare. GitHub one of the very few services I find to be worth paying for. I wouldn't be nearly as attached to Git as I am if GitHub didn't exist.)
Hosting your own Git repository is not an overly complicated affair, and even if GitHub did not exist, what would be the lure of an alternate content repository mechanism?
But, Github really handles the social element of code well. I really like how they encourage forking & collaboration.
They also provide an issue tracker, wiki, and some webpage functionality. All easy to duplicate, but it's even more trivial to sign up for a github account.
Think about that for a minute. Forget which dvcs tool they're using. You want to know why launchpad and bitbucket don't have the same uptake? It's not the tool. It's the fact that, as a maintainer, I can easily accept contributions from anyone who wants to submit a pull request. As an end user, I can IMMEDIATELY start hacking on some project with a simple click of the "fork" button.
THAT is the power of Github.