Isn't that graph hopelessly tainted by eg. the dominance of WordPress? I mean, yes that's PHP, but just because 80% of sites are running it doesn't mean 80% of development is in PHP. Far from it.
All those kind of charts have the same problem. It’s like asking “what food do people like the most?”, and answering “rice” because so many people eat it every day. The problem is that the question is so vague you can answer it many different ways, and all of the answers are correct.
What people usually mean when they use those stats is “look how popular my choice of language is”.
It is, but discounting PHP because of WordPress from that graph is still interesting - I doubt there are free one-click installs for ASP.Net like there are for WordPress for example, but are there for Ruby on Rails?
The comparison does not make sense. WordPress is a CMS that happens to be written in PHP, while ASP.NET and Ruby on Rails are frameworks for building web services which don't do anything by themselves. At best you would get a blank "Hello world" page and nothing more from a "one-click" installer.
What people usually mean when they use those stats is “look how popular my choice of language is”.