I've looked on various occasions over the last year or so but I've never discovered the difference between a Document Library and an Area Document Library on a Portal Area.

Go to the Create page for any Portal Area and you will see...

Document Library

Create a document library when you have a collection of documents or other files that you want to share. Document libraries support features such as sub-folders, file versioning, and check-in/check-out.

Form Library

Create a form library when you have XML-based business forms, such as status reports or purchase orders, that you want to manage. These libraries require a Windows SharePoint Services-compatible XML editor, such as Microsoft Office InfoPath.

Area Document Library

Area Document libraries are folders that make it easy to share documents with others. Each library displays documents in a list that can be filtered or sorted.

Portal always seems to overcomplicate things but maybe there is some difference I didn't notice. Can anyone articulate how these libraries are different?