Strange, I was at a business event yesterday and was able to speak to a few developers and also some high up folks from EA as well as Konami. As it seems, the X-Box has a remarkable "lower" pixelfillrate than the PS2 has (apparently, the numbers that Microsoft is publishing are wrong). This might be a reason, why there is no "grain" effect in the X-Box version of Silent Hill 2.
And before anyone starts, no, the PS2 doesn\'t use this effect to lower the quality of the textures. If you play through the game, you can switch of the grain effect.
Take what you want with this info. This has been said by EA and Konami also said something in that direction.