In response to the anonymous re-opener: you are misunderstanding the purpose here. Let me explain:
The login view is designed to be as customizable as possible. When the default values are left alone, everything works as it should: the standard login template is used, and the template is passed a context variable called "next" with the value of redirect_to.
When you start customizing things, redirect_field_name and redirect_to form the key and value (respectively) that get passed to the context. It's only useless if you forget to customize the template as well so that it knows to use your customized redirect_field_name instead of the default "next".
However, after some of the recent changes to that doc, I will agree that it needs just a few minor tweaks to be clearer on these points. I will fix it presently.