Great read, and an interesting warning sign about overly-controllable configuration files. If there's no conceivable good reason to to much of this, then the ability to do so becomes bad design that fails to protect your users.
The Postgres defaults in debian are understandably conservative to make it run everywhere. When I first installed Postgres I found it rather slow even on a good server. Only after reading guides on the web I found out why, the default RAM usage is limited to something like 32 MB which is way too low.