I think for most software on Github, the "end users" are themselves developers. Libraries, vimscripts, languages, programmer oriented utilities, etc.

I almost never got that sort of software from SourceForge. Most things that I have gotten from SourceForge are more "user application"-y. I can't think of any examples off the top of my head since it's been so long.. maybe things like Wesnoth.

Basically what I think I am saying is it depends on who the end user is.