As I replied to the other poster. I don't think DPI should necessarily be the exposed metric, but I do think that we should use something non device-dependent as our reference point, e.g. make 100% = 96 dpi.

I can guarantee that it is surprising to non-technical users (and a source of frustration for technical users) that the scale factor and UI element size can be completely different on two of the same laptops (just a different display resolution which is quite common). And it's also unpredictable which one will have the larger UI elements. Generally I believe UI should have behave as predictably as possible.