This is a great point. I work in biotech, and we use Python because of increasingly rich scientific tools available for Python. This makes Django (or another Python framework) the clear choice, just because it is Python.

Think about the whole language ecosystem. Django is just Python.

SO has 165,076 post tagged for Python. Just 65,706 for Ruby.

P.S. We are hiring Python/Django devs in SF. Email me if you are looking for a gig :) You get to work on a open source this project : https://github.com/iontorrent/TS/tree/master/dbReports

That's a very compelling reason to use Python if you need those things.

On the flip side, RubyGems is much bigger than PyPI and has a lot of modules that you won't necessarily find equal counterparts to in PyPI.

I think there's a lot of use cases one can come up with where one language's library offerings suit them better. That was how I chose between Ruby and Python. I chose Ruby+Rails but it very, very easily could have been Python+Django.