1.3 will support resolutions higher then todays HDTV standard, and it appears that the BLUE-RAY, HD-DVD may also support higher resolutions.
1.3 will match sound with images, ensuring that the response time for LCD, Plasma, Projectors and TV's are equal to that of the sound.
1.3 will also contain some more digital protection for HD signals, to prevent people from copiing them.