I think it's pretty simple, PS1 to PS2 were really goot advancements in technology, no doubt and disrespect that PS2 to PS3 is either. But let's say you grew up with PS1 and PS2 like me, PS2 managed to offer a lot more in terms of gameplay advancements, graphics, features and the like.
PS3/360 only expanded on that if you ask me, there wasn't much new, just better. New engine and new direction with IV and it seems to lose a sense of awe in my opinion. Each GTA had a very distinct gameplay style and IV lost that with it's approach to realism. I honestly like the new direction and I think it can mix the best of GTA III and the new realism element. TBoGT hinted that R* can achieve that.