Ruby and Python are two fairly evenly matched languages in their technical capacity. But Ruby is getting a lot of people excited, while Python (sniff) is lagging behind. This is partly to do with Ruby on Rails, a very easy-to-use and pretty, web-application platform. Python's equivalent major web-platform, Zope, was lauded as powerful, but is pretty heavy and bureacratic.
But might the personalities of the communities also play a role? MF Bliki: RubyPeople