You are slowing down the RAM, but when you increase the FSB, you increase the speed of the RAM. The speed of your RAM is increased along with the FSB. So if you set the RAM on a 333MHz divider, running with a FSB of 230, your RAM will be running at something like 185 or somewhere in that region. By increasing the FSB more, at some point the RAM will be running at 200MHz again, but the CPU will be running 400MHz faster than it does at stock. QED!
I know you read the OC guide, but I suggest you read some more, it seems you're not 100% up to speed on what factors are involved in overclocking.