WHY does an 8800GT crush 8600gt SLI'd?

Hello, just wondering the reason(s) why a single 8800gt apparently crushes 2 8600gt's SLI'd. I've read countless posts and articles stating how an 8800gt mops the floor with 8600gt's sli'd, but I cannot find anyone actually explaining why this is true.

Maybe I'm missing some obvious reason here, and if so I apologize.
Here's a comparison chart http://www.nvidia.com/page/geforce8.html

Is it perhaps the 8800 gt's 256-bit mem interface, or maybe the vast difference between their texture fill rates?