To OP, "hosted on git" and "hosted on github" are two very different things.
(Current first page: https://github.com/python-git/python/commits/master?page=117... )
Perl - first commit, 24 years ago
a "replacement" for awk and sed
(Current first page: https://github.com/mirrors/perl/commits/ams/no-more-study?... )
Apparently the current Linux kernel repositories don't go back as far: http://kerneltrap.org/node/13996
I wouldn't be surprised if it makes much less sense for the kernel, though.
Also, github is just a mirror. The main repo is on git.php.net where they are continuing to use their karma based everyone-commits-to-a-central-repo system (see http://git.php.net/?p=karma.git;a=summary). This goes together with the rest of the infrastructure that they continue to self-host