Why use Django on Google App Engine?
I am still very new to Google App engine development, but the interfaces Django provides do appear much nicer than the default. The benefits will depend on what you are using to run Django on the app engine. The Google App Engine Helper for Django allows you to use the full power of the Google App Engine with some Django functionality on the side.
Django non-rel attempts to provide as much of Django's power as possible, but running on the app-engine for possible extra scalability. In particular, it includes Django models (one of Django's core features), but this is a leaky abstraction due to the differences between relational databases and bigtable. There will most likely be tradeoffs in functionality and efficiency, as well as an increased number of bugs and quirks. Of course, this might be worth it in circumstances like those described in the question, but otherwise would strongly recommend using the helper at the start as then you have the option of moving towards either pure app-engine or Django non-rel later. Also, if you do switch to Django non-rel, your increased knowledge of how app engine works will be useful if the Django abstraction ever breaks - certainly much more useful than knowledge of the quirks/workarounds for Django non-rel if you swap the other way.
When researching Google App Engine (GAE), it's clear that using Django is wildly popular for developing in Python on GAE.  I've been scouring the web to find information on the costs and benefits of using Django, to find out why it's so popular.  While I've been able to find a wide variety of sources on how to run Django on GAE and the various methods of doing so, I haven't found any comparative analysis on why Django is preferable to using the webapp framework provided by Google.
To be clear, it's immediately apparent why using Django on GAE is useful for developers with an existing skillset in Django (a majority of Python web developers, no doubt) or existing code in Django (where using GAE is more of a porting exercise).  My team, however, is evaluating GAE for use on an all-new project and our existing experience is with TurboGears, not Django.
It's been quite difficult to determine why Django is beneficial to a development team when the BigTable libraries have replaced Django's ORM, sessions and authentication are necessarily changed, and Django's templating (if desirable) is available without using the entire Django stack.
Finally, it's clear that using Django does have the advantage of providing an "exit strategy" if we later wanted to move away from GAE and need a platform to target for the exodus.
I'd be extremely appreciative for help in pointing out why using Django is better than using webapp on GAE.  I'm also completely inexperienced with Django, so elaboration on smaller features and/or conveniences that work on GAE are also valuable to me.