Unreal Engine 3 was designed to run first on PC and was later ported to Xbox 360 and PS3. The Xbox 360 is very much like a PC while the PS3 uses the Cell Processor which is not like a PC. Without getting too technical, what that means is that it is easier, faster, and cheaper to develop an Unreal Engine 3 game for PC and Xbox 360 than the PS3. The PS3 and the Xbox 360 are so close in power that it is a wash. The reason that Uncharted, God of War, and The Last of Us look so good is because Sony invested huge sums of money and put an enormous amount of effort into their 1st party graphics engines. That was not seen on Xbox 360 until Halo 4 which is on par with the best of what PS3 has to offer graphically. It's not that the PS3 has power to spare and 3rd party devs are too lazy to polish their games. It's that the PS3 is difficult to work with and unless Sony decided to hand out free samples of the the tricks they use in their 1st party games 3rd party devs have to work harder, longer, and spend more money on PS3 ports than PC/360.
