For the rationale behind it, read this article by Larry Wall ... http://www.wall.org/~larry/pm.html (really, it's one of the best language-related essays around).

     Contrast with Python, where "There should be 
     one - and preferably only one - obvious way to
     do it".

As a Python developer myself, I call that bullshit ... how about 2 urllibs in the standard library, both broken and a dozen or so XML parsers and I still have to install PyQuery to remain sane.

Also, its one obvious way to do it also breaks down in the language itself, like there's still a difference between old-style and new-style classes. And because the language does not have anonymous code-blocks (something which Perl has), the language designers added a bunch of features to take care of certain use-cases, features which are not orthogonal, like lambda expressions, foreach blocks, with blocks, iterators AND decorators, all of which could have been avoided by adding just a simple feature.

If you ever try building a simple DSL, something that modifies a class at runtime, you'll have about a dozen or so techniques to use, but none of them as beautiful as ActiveRecord ... which relies on the fact that a class block in ruby is just syntactic sugar for opening a class context with define_class and passing it a code block.