If you don't like pull requests, you can use GitHub as nothing but a git remote. If you use https://github.com/defunkt/hub, you don't even ever have to visit the GitHub website once you've signed up.
GitHub does enhance and doesn't replace git. You're proclaiming an "embrace, extend, extinguish" when the fact is that nothing on GitHub is incompatible in any way with git off of GitHub. If one day GitHub were to torch their servers and disappear, all I'd have to do is git push to another remote and we're back in business. I'd lose my issues, but git doesn't exactly ship with an issue tracker.