I think you're comparing apples and pears when you talk about Maps. There's a clear use case for scrollbars on vertical documents (i.e. most of them), and even when viewing something in an infinite scroll, so you know where you are when scrolling back up. (Although don't get me started on the UX of infinite scrolling!)
Edit: Thinking further about this, the affordance for maps is a change in the cursor to a grabbing hand. You have to learn that, but there's a clear visual difference in the cursor to show that something differnt happens there.
