This is true but very limited as well. GitHub isn't used for just git now, it's also an issue tracker, a wiki (yes, those are repos as well, but you don't usually have them sync'd), Github-only services (e.g. Travis), package managers (e.g. Cocoapods and Crates).

There is a lot riding on GitHub that developers use. Hell, even closed-source companies sometimes use empty GitHub repos so they can use Issues for openly available tracking.