If you can imagine a helicopter scooping up these cars going at 10mph and whisking them to their destination, you have a rough notion of what CPUs have to do nowadays to keep themselves occupied most of the time. The software manufacturers know that, too, and they help that process along by essentially putting their codes in relatively small chunks that the CPUs can wisk away. Sort of like putting Honda Civics rather than big tractor trailers on the road for the helicopter to pick up. Most importantly, this approach works fine for most current software most of the time. This is the primary reason why DDR doesn't help much for most applications.
Faster memory is still too slow for CPUs.
This is a big reason why the current Willamette doesn't do too hot. Now yes, there are applications that by their very nature should be able to use all the memory bandwidth they can get. These are the farmers. However, just like farmers in most developed countries, there aren't too many of them around. Video editing is a good example of this, games at least theoretically should.