A AMD processor works differently to a Intel. AMD runs alot more efficiently, having smaller pipelines so it can do more per clock, and because of the smaller piplines in runs alot better in games, as AI isn't a written script so some calculations are discarded, and an Intel would have wasted alot more time than a AMD. AMD also makes a huge difference between intel with the onboard memory controller, so it doesn't need to go through the extremly slow memory controller on motherbooards. This onboard memory controller allows bandwidth of up to 6.4ghz when the RAM is run in dual channel with the memory at PC3200, Intel doesn't give twice as much bandwidth when in dual channel.
All this put together makes AMD so much better at gaming than the equiverlent Intel, but at alot less.
Here is the benchtests: