That's why many people (I first read about this in Alan Cooper's About Face 2.0) advocating for automatic save also advocate for unlimited undo (or at least something close to it) because closing a document and not saving it is just a form of undo while closing a document and saving it should be the default action.

This is also a place where the desktop metaphor (with paper documents) around which most WIMP systems are built exposes computer details and fails to stick to its metaphoric roots. When I scribble something on paper it's there and I don't have to consciously remember to somehow commit a transient state of my scribbling to paper explicitly.