It's always amusing that whenever somebody says things like this, PC haters start freaking out.   

While I'm not a graphics whore and I'm fine also with mid-entry level GPUs and CPUs, bigger main RAM benefits FTW, they include, as some of you just wrote, being able to manage bigger maps and worlds, more players at once, and also, I add, more objects, more NPCs (this applies more to single player, but also to MMOGs), not only in the whole map, but also simultaneously in a single scene. If big RAM is helped by powerful CPUs and GPUs too, to all this high detail and graphics quality can be added, making happy both graphics whores and gameplay fans.

Stwike him, Centuwion. Stwike him vewy wuffly! (Pontius Pilate, "Life of Brian")
A fart without stink is like a sky without stars.
TGS, Third Grade Shooter: brand new genre invented by Kevin Butler exclusively for Natal WiiToo Kinect. PEW! PEW-PEW-PEW!