Why does PSP being backwards compatable even matter? PSP vs GCP = GCP get's crushed by Playstation's hype and anticipation. Not to mention without all the hundreds of gameboy games being able to be played on the system consumers wouldn't have such a sweet option as that to buy GCP instead of PSP.
Hype and anticipation doesn't carry through. Look at the movies this summer. Many of of the big buget movies that have been hyped for ever did horrible at the box office. Same holds true with handhelds. Hype will get you through the first few months . After that sales will drop drasticly if its a bad product or there is a better product out there .