alt Hacker News> 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.
When OS X was new, Apple was still under the assumption that Java on the desktop was important, and they built an in-house Java with full Aqua support. It was still _terrible_! All the Aqua-specific affordances like animation or shadows were janky or absent. Sizing and positioning always felt weird because the application was written assuming Windows-shaped controls.
Basically, cross-platform GUI only looks good on the platform that it was originally designed for. Unless the other platforms make zero interesting choices, they will always look worse.