Allrighty... here we go...
First off, you need to know how DDR works. The communications bus to the RAM is operating at 200 Mhz, (what?!?.. it's true.) The way you get 400 MHz is the same way you get AGP x 2. Instead of sending 1 bit of information on the enire cycle of a wave... Information is passed at the rising AND falling edge. This makes it SEEM like 400 MHz, but you are still at 200 MHz operating at twice the efficiency. Here is a good link for details. How DDR works
Now DDR2 (like AGP 4x) transfers data at the 3/4 rise, peak, 3/4 fall, 1/4 fall, trough (bottom) and 1/4 rise. This RAM is STILL at 200 MHz, but it quadruples the efficiency. Dual channel is like making a RAID 0 for the RAM.
Ok, so now that we know this RAM works at 200 MHZ, now to answer your question.
The Hammer's, like all processors, are made up of more then just a Processing Unit. You have a hyper transport interface, Northbridge, Control Logic, JTAG Debug and some other options. This is why you have a Clock multiplier!!!
The only reason the CPU core and the L1/L2 cache can operate in the 2+ GHz range is because they are so close together and quality/uniformity can be controlled by processor manufacturers to push the CPU cores to the edge.
Here is a link to AMD's site on there 940 layouts. (The 939's have the same Core). Look on Page 9.Core Layout. (Go to page 9)
Plus the data paths are so small on the CPU that internal radio frequency interfearance isn't an issue. You try to push that frequency through circuit paths on a motherboard that are allmost 1000000 times wider, the RFI would be so bad you could probably cook your neighbors potatoes. And these are the data paths that the CPU must TALK to. A non uniform, big fat and lazy pipeline connecting PCI, AGP, IDE and a whole bunch of other abbreviated name components together..
Lets pretend frequency is water pressure, and bandwith is how wide your hose is.
In both instances you want to get something from point A to point B. You can get the same ammount of water at 100 PSI through a 1/2" hose as you can with a 50 PSI 1" hose. The memory controller dosn't need to run greater then 200 MHz because it uses bandwith, not frequency to pipe data.
In a nut shell, you are not missing something. About 1/2 of the processor operates at 200 MHz, and the rest of the processor operates at whatever it's rated to.. ie 1.4-2.6 GHz.
Dual AMD MP 2800+ OC'd to 3.08 (140 x 22) Dual Vapochill
1024 MB Kingston DDR Reg ECC 3200
Radeon 9800 128 Vram
2 x Maxtor 80 Gig ATA 133 8 M cache RAID 0
2 x Seagate 'cudas 80 Gig ATA 133 8 M cache RAID 0 (Swap + Junk)
1 Seagate 'cuda 80 Gig file storage