Why is Ruby more suitable for Rails than Python?
The real answer is neither Python or Ruby are better/worse candidates for a web framework. If you want objectivity you need to write some code in both and see which fits your personal preference best, including community. 
Most people who argue for one or other have either never used the other language seriously or are 'voting' for their personal preference.
I would guess most people settle on which ever they come in to contact with first because it teaches them something new (MVC, testing, generators etc.) or does something better (plugins, templating etc). I used to develop with PHP and came in to contact with RubyOnRails. If I had have known about MVC before finding Rails I would more than likely never left PHP behind. But once I started using Ruby I enjoyed the syntax, features etc.
If I had have found Python and one of its MVC frameworks first I would more than likely be praising that language instead!
Python and Ruby are usually considered to be close cousins (though with quite different historical baggage) with similar expressiveness and power. But some have argued that the immense success of the Rails framework really has a great deal to do with the language it is built on: Ruby itself. So why would Ruby be more suitable for such a framework than Python?