> cross platform GUIs are ugly by default, compared to fully native desktop apps, because they don't entirely replicate the affordances or the style of the platform;
I think this is an implementation detail. It's up to the software stack whether it leaves off before drawing the UI elements on screen, or goes ahead and takes on that responsibility too. The wxWidgets toolkit uses the runtime platform's UI, so it does not draw the widgets themselves. Java Swing took on the task of drawing the UI elements on the screen in its own style.
I think this is an implementation detail. It's up to the software stack whether it leaves off before drawing the UI elements on screen, or goes ahead and takes on that responsibility too. The wxWidgets toolkit uses the runtime platform's UI, so it does not draw the widgets themselves. Java Swing took on the task of drawing the UI elements on the screen in its own style.