Having Google Analytics on a website does not make the people working on that website JavaScript developers. For many projects, JavaScript is tacked on, usually via a designer doing some tricks in jQuery.
Github's numbers are going to be biased towards programmers who use languages that are more progressive. .NET developers aren't using Github and neither are many older companies that are still using self-hosted SVN and CVS repos.
".NET developers aren't using Github" says who? I find about 80% of open source projects for .Net on Github. With the other 20% being split between codeplex, sourceforge, Google Code, and self-hosting/publishing