PC games are costilier(some of them) 'coz, when the Game Developer makes a game they have to TEST it for different PC Configuration, so that the Game is able to run on a Nvidia/ATi/Intel Chipset/Gfx. card without a problem.
& when it comes to PS2, the Game developers dont have to go thru any trouble
, as all the PS2 have same hardware/coding stuff.