Sure. But, for instance, is Django as tied to the active record pattern as is Rails? And yes, I know you can swap out persistence layers in modern Rails, which is good (because active record is utter bilge), but who does that?
No, it's not. But since Rails 3 neither is rails really. Rails is more about the ActiveModel pattern, which has it's own API. Active Record inherits from ActiveModel. You can pick and choose what you want in your persistence classes, or even better, make models/classes that have no persistence layer tie.
For instance, if you want to use a class like it was a MySQL table, you could include a few ActiveModel classes which will make things for ActiveSupport helpers work with them.
Maybe I misunderstood your question. If you're looking for reasons to pick one over another, then it's whichever language you know best.
Web frameworks really only differ in philosophy, and in this case, both are batteries-included, monolithic frameworks. They are practically identical solutions.
Philosophically they're quite different. Every layer follows a different approach: templates, controllers (views in Django), urls, model definition, ORM etc. A lot of this comes from the core philosophies of the languages, whilst Ruby and Python may be closer to each other in philosophy than either are to say Java, they still have substantial differences.
&c.