iPaq screen format and GameAPI

The iPaq has a 4096 colour display (4 bits each of Red, Green, and Blue). Yet my application which uses GameAPI reports a pixel format of 565. All the drawing code goes through my 565 pixel plotting code, and is correctly drawn to the screen. Why is this? If the video driver is doing some internal conversion, it seems a waste of time when it could have reported the native 444 format in the first place.<br><br>Any ideas?