I brought up the TIOBE index not as an absolute metric but to show that Ruby and Python are not totally obscure languages and have usage similar to PHP. I think your "go into any web-dev shop" test fails for software of interest to developers here who are developing web applications rather than dynamic sites. The web-specific part of PHP is it's ability to act as a template language, inline with HTML. I don't think this is an advantage for web apps as there is often significant logic and infrastructure other than the user interface and frequently several interfaces are desirable (e.g. API, mobile, and web). Mixing together logic and presentation, that is to say the web-specific parts of PHP, make this goal much more difficult.

Ruby and Python were not originally made for web development, but they have been extremely successful and popular in that role. Twitter, Github, Stripe, and Hulu have significant Ruby components, and Instagram, Dropbox, Mixpanel, Pinterest, and Yelp use Python. There are smart people choosing these languages to build their companies with for a reason.