There are 2 things that you need to be aware of:
First of all, AMD CPUs use Hypertransport which opens a huge amount of bandwidth to the memory. Along with this is AMD's on-die memory controller that reduces the time needed to get information from the RAM to the CPU itself
Second, AMD CPUs process more instructions per clock cycle. This is why a 3000+ @1.8GHz competes with a 3 GHz Intel. I'll give an analogy:
Two runners are running in step with each other. Their feet hit the ground at the same time as the others do. Imagine that one runner is taller than the other. The taller one is going to cover more ground per stride than the shorter one. Now if the shorter runner wanted to keep up with the taller runner, he would have to run faster by moving his feet faster just to keep up, because he covers less distance per stride.
Short Runner=Intel CPU
Tall Runner=AMD CPU
Stride Frequency=CPU Frequency
Hope that helps