Couldn't tell you why they choose to do it that way, it's just the way it is. I believe it had something to do with the fact that DDR2 is two channel, and it's 800mhz per channel, but you still multiple the DDR3 by two as well... so who knows. Not me, I just know that you multiply it. (want to learn more? Google it :P) About the 1333, it shouldn't say that. Might be a mobo limiting issue? What mobo do you have. Can you change it to 1600?