What is it with these mainstay frameworks that they never adopt the mature ORM on their respective platform but instead keep growing their own, less than half-baked alternative? We have this in django vs SQLAlchemy and Rails vs datamapper. The arguments that I've heard were mostly that the respective ORMs either weren't around when the framework started and/or that anyone "can just plug their preferred ORM in anyways…
* I love Django's ORM, too. It's far simpler, much easier to teach to new users, and results in code that "scans" better. It's only able to achieve that ease-of-use by sacrificing features -- a classic trade-off. Neither approach is more "right."
* SQLAlchemy didn't exist when we wrote Django. Yes, you've just dismissed that argument, but I can't. There are thousands -- probably tens of thousands -- of Django sites out there, and I'm not so quick to break backwards compatibility just for the new shiny.
* Finally, and most importantly, SQLAlchemy has some fundamentally different goals than Django's ORM. SQLAlchemy aims to provide an API to represent SQL in Python. Django aims to provide a persistance layer for objects. The difference between these philosophies is important: the use of a relational database is almost an implementation detail for Django, but it's SQLAlchemy's raison d'être. This isn't just academic: it means, for example, that Django's ORM will one day support non-relational databases (work here's already begun), but SQLAlchemy won't.