800x480 is the native resolution of the Lilliput/Xenarc LCD panels.
If you've ever seen a desktop LCD, you will know that it is MUCH crisper at it's native resolution than at a non-native resolution, as when it's in it's native resolution, you are mapping pixels 1:1, but when it's non-native, you may be trying to display 1 pixel of the signal in 1.3 pixels on the display, which it can't, so it "blurs" them together, making the picture less clear.
Therefore, the perfect resolution to run on the Lilliput/Xenarc is 800x480, to get that 1:1 pixel mapping
The screens are actually 15:9, not 16:9, like "Widescreen" TVs etc are.
Garry