under Pages Administration there's "Page Type Concept" but when you create a new page and select any type, it creates a page with one field in it of that type. So seems like those should be called Section Types.
A new page has to have at least 1 section. So the "page type" you choose when creating a new page, is strictly speaking a page with that particular section type. You can also add new sections to any page.
For example I found a news blog module where you create a page of type News, then click an Add button while to add posts to that page. So that content is not part of the tree, it's sort of governed by that particular section/module.
That's correct. The news module is the content type you see in the page tree, not all individual news items. You can administer those from within the News module. I would say that is pretty standard
