The 16:9 Settings would be for devices with 16:9 screens. Pocket PC's use the 4:3 aspect ratio, Just being sort of rectangular doesn't automatically make a screen 16:9. There are plenty of rectangular shaped TV screen that are 4:3. I wish I had some technical explanation for you but I don't.
and the guy who designed betaplayer is still on vacation. Maybe PocketTV Team can explain...