This is not true with common applications people are familiar with. Excel and Word will happily "save" a PDF, and it behaves like exporting and doesn't change the document being edited.
Word and Excel seems to change behavior on every release. I don't think it's something Gimp should try to chase.
Gimp has save: "Save native gimp file" and export "Export an image file". It's a bit confusing to me why people find this confusing.