50 million PSPs have been sold. I don't believe most of them were drawn to PSP for its quality and fidelity to the home console experience. I think a lot picked it for its media capabilities - it had a strikingly good screen for its time of release, and was price competitively with things like Archos while also offering other entertainment functions including games. PSP is no longer the only full media platform; they can
all do everything. Meaning now the reasons to own a PSP, for gaming, films, music, web browsing, all in one package, are no longer reasons to get NGP when your mobile already does that, including GPS, internet access, yada yada. The only differentiator now is the game potential, which won't appeal to everyone. So how many of the 50 million PSP buyers care for twin-stick shooters and Monster Hunter? If 10 million, that leaves 40 million without a particular tie to NGP. Thus we can't look at NGP even repeating PSP's respectible success, unless tens of millions of console gamers also want to play those same games on the go Which we can be confident isn't the case given existing console gamers saying, "I want to play those experiences on my console."
In a way it's like PSS is there to shore up the probably titchy market, with developers being told they don't have to target a small user base but will have a huge one, with Sony able to invest in PSS exclusives to single-handedly try and attract buyers with titles like Uncharted and LBP.