That seems wrong. If a phone is held vertically, the 768 pixels is the width, not the height -- so the buttons take a chunk out of the 1280, not the 768.
Sure, but I don't think anyone is worried about maintaining a perfect 9:16 ratio for reading text or what have you. Generally when a device like that starts playing 16:9 content it forces a switch to landscape mode with the content centered and at the top, leaving a 1280x48 swath on the bottom for the home bar and the top 1280x720 for native-resolution 720p content.
