I've watched the ecosystem from the pre-1.0 days and it is still steadily evolving. New packages are being developed (and abandoned) every day. Some of them are very mature, others are just starting, and many are just plain bad.
Implementations that stand out, like south, may get incorporated. Especially when they're valuable to the core of Django; all may not agree, but migrations (and class based views) should have been in there from the start.
Others depend on your needs. Don't force me into using TinyMCE as a rich text editor, I'll regretfully make that decision myself. I want to choose the best available package for my CDN host. I'm switching thumbnail processing engines because mine hasn't been updated in over two years.
Importing all of my models into the shell is best left as an explicit modification for those that want it. If it was a good idea, why wouldn't Django do it by default?
Reasons to use Django over other, lighter frameworks:
* The ORM
* Forms – The ORM
* contrib.admin
* Authentication
* Extendable command line interface