I think the expectation is that Polyphony were going to make a Gran Turismo game on PSP, not a watered down version of a PS2 game.
I'm pretty sure people loved Resistance PSP and GoW chains, because they were designed for the handheld. By the looks of things, GT PSP was just GT4 shoved into a UMD and what ever didn't fit was discarded without much thought about which parts would be more crucial to core gameplay experience.







