i'd guess a mixture between stardards, and prise. i'd guess the higher-resolution displays are much more expensive to produce..
oh, and, another point: normally, you're closer to a notebook screen than to an external screen, thus, the resolution doesn't have to be as high.
oh, and.. if you want to see a real nice resolution screen, check out the new toshiba libretto. it has a 7.2" screen with 1280x768 resolution.. jummie