GitHub is slowly starting to reflect the software world at large, although the true picture is Java and C leading by a huge, huge margin. I don't expect GitHub to ever fully reflect that, as most Java shops, and nearly all C shops, would never host their code on GitHub.
I think it's safe to say that most projects on github are libraries and snippets, not finished products. Not even Ruby shops push all of their actual work to github. But at least there is a culture of sharing libraries, which drives the Ruby % up, and I don't see this happening a lot with C.
