Have to agree with others here. All the other PS2 HD Remakes have had Plats (even when bundled on one disc each game has a Plat).
As others have pointed out neither price, length or distribution method seem to be a deal-breaker here. It really does seem that they decided to apply MS Live policies to PSN and save some cash.
It's a shame - but that said, those people that are refusing to play the game because of this are missing out on one of the best adventure games of all time.