It's so weird. Git's major differentiating feature is that its distributed nature means you don't need a centralized server, and your work isn't blocked if that (unneeded) centralized server goes down. Yet, so many developers have twisted git around to make it a centralized single point of failure--on purpose! I don't understand it.
Git still works offline when github is down. Try committing or getting history when the svn server is down, let alone pushing to a different remote. The things github centralizes are the things that aren't actually git itself.