In a related vein, the idea reminds me of a strain of computer graphics research known as "non-photorealistic rendering"[0], i.e. acknowledging that for some uses, building a full shading model and trying to mimic reality actually makes the image worse rather than better. Once you've made that realisation, you can design renderers that have flat shading or heavier outlines or any number of other features that make it look more "diagrammy". I guess that xkcd graphs (and napkinlaf) are arguably themselves instances of NPR.