I think the answer is you're not supposed to be watching both screens, the touchscreen is meant to augment the main screen by having maps and inventories and stuff like that. The touchscreen means you can also select these things really quickly by just pressing it without having to go down-down-left-left-left-down-select.

Having said that I'd like a PSP because I like the games on it more. Although I'll never buy one.... with my own money.