Macbook Memory Clock Speed

Since the new MBP's have an 800 MHz FSB, why is apple installing memory whos limit is only 667 MHz? Do I not understand this concept or can you get upgraded ddr2-800 pc6400 memory from the existing ddr2-667 pc5300 memory to make full use of the FSB speed?

I was wondering about that too.

There is no memory yet that can utilize the new 800mhz front side bus. At least not that I know of.