I had the same problem as #6 too (Heroku forcing you to install psycopg2 even though you're using a different database). The reason for this is because Heroku post-deploy script reads the DATABASE_URL config variable (which defaults to Heroku's Postgres shared database) and inserts it automatically to your Django database settings.

If you want to use a different database and not want to be forced to install pyscopg2, what you have to do is change that DATABASE_URL variable to something that corresponds to your database, and Heroku will act accordingly.