They didn't forget, you don't connect directly to any database directly from Flex. You need a middle tier (java, python, php) that brokers requests between the db and the client, and handles authenticating the client.

The good news is that Postgres is really good for working with XML as is Flex, so your middle tier can be much smaller than traditional web programming.

I cover Flex, Postgres and Flex in my blog and you may find this article of interest.
XML in Postgres – The Game Changer Flex and Specs()