The vast majority of projects on github also do not pay. The two major features you pay for on github are larger repositories, and private repositories. The free offering is good enough for almost all open source projects.
In terms of PortableApps.com, I don't think we'd be a good fit for GitHub since we're a project that's a conglomeration of apps made portable (for USB and cloud use). I think we're around 90TB of bandwidth for downloads in the last month for our open source apps via SourceForge (some of our open source apps the publishers self-host like Inkscape and LibreOffice so we don't push those through our SourceForge project).
Surprisingly expensive business.