[greendata]

You'll definitely find specialists in python but they'll also be experts in specific frameworks or packages like Django/Pylons/Pyramid etc. I'd say the same thing goes for ruby...if you're a ruby expert it's almost explicit that you'll at least have an intermediate knowledge of rails.

[pottereric]

Agreed. The ruby expert will probably also be proficient in HTML, JavaScript, and CSS. You need a range of skills to be an expert in something.