I see what you're saying, but I think there are two major use cases for Github, one where the README should be first, and one where it should be last. The first is yours, visiting a repo, which often serves as de facto homepage for a project. The second though, is for projects you contribute to or use frequently, where finding out what's new or navigating to particular piece of code is the most important task. I'm not sure what a good way of distinguishing between the two would be.