That's the difference between reference documentation and introductory documentation. You go to reference documentation when you want to look up the details of something you already know; you go to introductory documentation if you want to learn it for the first time.
Okay sure, but how do you get from the introductory docs (which are far and wide, as well as lacking in quite a few areas) to reference documentation. I can see how ruby-doc can be a good resource but only for those that know the language and know what they should be looking for, even then though sometimes docs like python's are better references.
there are also two great books, the agile rails book, and the rails way. They will get you started, and may be 90% of what you need. The docs are good for the rest.
One thing though, we're comparing apples and oranges; the docs for a web framework vs the docs for a standard library. Are the django docs similar to the standard lib docs?
I'm not trying to dis python, I really like python and use it whenever I need to do mathy stuff with numpy and scipy. Most other things I do in ruby.