Of course, I may be wrong because I last played the game two years ago on the PS2 when I replayed through it.
But I didn't find the PS3 version noticeably harder. Of course, I may be wrong but I remember close to release that people were claiming that it was just the PS2 PAL version.
There were content differences between the ICO (and I think SotC as well) PAL and NTSC versions. So people claiming it was based on the PAL versions were probably talking about the content differences and not the physics.