Another big advantage of Git for sites like GitHub is that you are never putting your eggs into one basket. You have your local copy of all history in a project. GitHub is merely a mirror. Sure, some features have been sprinkled on top like pull requests and an issue tracker, but those are not the most critical part. If GitHub goes down you can move your whole Git history to another site like GitLab, sourcehut, or just self-host it, or you can even start doing it right now with minimal effort. This was never the case with CVS and Subversion.