One of the goals of git is to be decentralized. If Github is to be the … hub of git, then maybe it could take into account that there are other hubs out there, and allow pull requests to happen on git URLs that are not hosted on github.
The documentation is fairly clear about this: pull requests require that you have a Github account and that you fork a repository on github. Is this a real current technical limitation or is there a way to workaround that on Github?
If not, is it eventually planned to allow Github's "pull requests" tool to actually allow to pull from repositories outside of the Github silo?