The original Palms had screens that were 160x160 pixels. Even the most recent Palms have 320x480 screens - half of a standard VGA screen, which almost no modern desktops bother with these days. Viewing large panoramas, or even pictures with decent resolution, just doesn't work. Text can be very nice, and simple graphics tailored to the limitations work well, but many typical desktop apps are practially unusable at 640x480.
You don't really want a large, high-resolution screen on a PDA anyway, at least with current technology. They suck battery like mad, and are too large to be easily portable.