The CalDAV server authored by Apple and included with OS X Server is written in Python. PyObjC receives a lot of attention from Apple employees. I don't think there's much preference exhibited by Apple one way or the other.
And vice versa, there must be some Linux distros that have tools written in Ruby, right? Particularly some of the newer ones, I seem to recall hearing that their system tools were Ruby.
As I said, it's just a slight preference. But I look at things like the official Apple support for MacRuby (Apple is employing Laurent to re-implement ruby in Objective C, so that ruby objects are Objective C objects - you'll be able to program Cocoa in Ruby without having to take the performance hit of crossing a scripting bridge all of the time!), and I don't see a commensurate support of the Python world. But as I said, it's only a slight preference - Apple s evidently right behind both languages, as they make leveraging the power of OS X so simple.
Counter-counter: Podcast Producer is a Rails app. I think Apple is just letting their employees pick their tools (at least for server apps) as they see best, rather than arbitrarily enforcing the choice of a single language.
And vice versa, there must be some Linux distros that have tools written in Ruby, right? Particularly some of the newer ones, I seem to recall hearing that their system tools were Ruby.