[abusque]

You can filter these out actually. When you go on someone's profile, and then to the "repositories" tab, there is a drop-down menu that reads "Type: All" from which you can select other repository-type filters, namely forks, mirrors, and sources (the user's own repositories).

It's somewhat imperfect as not all forks or mirrors are marked as such by github (if, say, it's a fork of a repository not originally hosted on github), but it works in the vast majority of cases.