Document Libraries vs. Area Document Libraries

Saw something that made my head turn with SharePoint so wanted to throw it out there.

At the portal level you can create document libraries, lists, etc. in an area. The golden rule has been (and a contention of FAQs all over) is that content in an area uses the permissions set from the area. This is in contrast to a WSS site where the permissions can be applied to each document library differently as WSS sites have no concept of an area.

However in the creation page for an area there's a new option. You can create a Document Library AND you can create an Area Document Library. I wondered what the difference was. A quick Google-is-your-friend search turned up a message by someone saying that Area Document Libraries use permissions from the area whereas a document library in an area can have it's own permissions set (if you can follow that logic) . This however is not true because a test creating these things in the same area show the option to set permissions still isn't there for either library (at the portal level).

So the mystery is still unsolved? What's the difference?