Just to point out that all those objections could be made about Django as well.
Also, in Django models are explicitly defined. There's no ActiveRecord magic of reading the database to define the model. Which is not to say that AR's approach is bad or wrong, but it is pretty significantly different from Django.
Further smaller changes have been made since then for the same purpose: explicit over implicit, code or configuration over convention is part of Django's philosophy.
IMO that also makes it easier to graduate from a beginning to an intermediate level use of the framework because while there are sane defaults in many places, in others you're required to define your specific implementation explicitly from the start. It's a tiny bit more code up front, but all the details are exposed and it's obvious how to override default behavior. And at the same time the framework supports keeping your code reasonably DRY and takes care of much of the tedious, repetitive stuff.
There's still tight coupling in some places (ModelForms, for instance, are arguably part of the controller layer and are tightly coupled to the ORM). But they're reasonably optional (you can use plain Django Forms instead of ModelForms in your views or not use the Forms library at all.)
My experience with Django (for instance: class-based views and admin parts) is actually that you have dozens of magical classes or methods and if you don't know them all, you're screwed. Often when I try to do something, many aswers on StackOverflow boil down to "just override a_method_that_is_hidden_somewhere()" or "just use ListButWithSpecificBehaviorView(), easy you see?".
Are there any specific example you have in mind where Rails do something magical that requires more code in Django but where Django is more explicit?
PS: not trying to start a flamewar, both are OK-frameworks, bla bla bla ;-)
I feel like people really forget what it's like to be a beginner when they say "read the source".