Ruby, for all the problems it can cause, gives you. More than one way to solve a problem. Yes, it sometimes makes it harder to dive into other's code but I happen to enjoy the expressiveness.
Mind you I love some of the things about python too. Namespacing being one of the primary ones. Another is that, short of advances pythonfu (like django does), I can usually pick up someone else's code and dive right in.
Python has amazing access to mathematical and scientific libraries as mentioned. However with ruby, I would punt to the Java ecosystem via JRuby if I needed that.
It's a lot like design patterns. Some patterns don't fit in all languagea but that's usually a case of the language itself giving you another way. Mixins in ruby are a good example.
With Ruby, the flexibility of being able to do things in more than one way makes it necessary to learn conventions rather than just the language spec. Sometimes breaking those conventions can have a tremendous upside. Some people find that upside worthwhile and others don't.
