Just looking at the python/ruby communities mostly from the outside, I wouldn't discount that many python folks dislike Git simply because many rubyists like it. I'm not saying there aren't valid technical reasons, (and frankly I don't know much technically about either Git or Mercurial) but I'd be surprised if emotion/religion doesn't play in at least a little bit.
You "guess"? That's not a very accurate analysis of the situation.
Since they aren't sharing any of these details, we have no choice but to assume there are none. In fact, their exact reason for not using Git was "it also provokes strong antipathies". That doesn't even _imply_ technicality on any level.
Either way, I couldn't care less personally. The only people they're hurting are themselves, as a gateway can be created between Git and Mercurial. All the projects I work on right now use SVN, and I just use git-svn for everything.