I don't know anything about that graph, but I'd be happy to cede the point that there are many more installations of PHP than Ruby/Python on the web as long as you'll cede the point that this fact doesn't relegate them to "tiny niche languages."  If you don't agree, let me know and I'll argue that point.<p>Obviously what you choose to use for development is your decision.  That said, I am confused as to why it's so important to you that you use the most popular language.  After a certain threshold of popularity, it doesn't seem that it should matter.  PHP, Python, and Ruby all have the critical mass of developers and library support needed to render language popularity concerns irrelevant.