DDR3 isnt tripple anything, Take DDR @ 200mhz (DDR400/PC3200), and you'll get 3200 bandwidth, DDR2 @ 400mhz (800DDR2/PC2-6400) and you'll get 6400 bandwidth (twice the chip frequency compared to DDR memory hence twice the datarate as well).
DDR3 on the other hand, at 400mhz (800DDR3/PC3-6400) is exactly the same bandwidth as the DDR2.
The big advantage of DDR3 is the fact that the interface is greatly improved over DDR2, allowing much higher clock speeds, hence 1600-DDR3/PC3-12800, and even faster are possible, while DDR2 pretty much maxes out at 1150/PC2-9600.
They are all 64bit busses (per channel), and they are all double datarate/bandwidth.
The only time tripple comes into play is with an i7, with a tripple channel controller, but with the i7 its not changing the clock speeds or datarate, its simply using a 192bit wide memory bus. But even then you still should get 667mhz displayed with CPU-Z for DDR3-1333.
Memory bus can be as wide as the chip makers desire, hence on graphics cards its often 256bit or even wider, but making the bus wider makes the PCB design much more complex and expensive. Hence the price of X58 boards. The only way to get more bandwidth without the excessive cost of wider and wider busses, would be to go to a serial bus design, but the odds on that happening anytime soon are pretty much zero, as Rambus would jump on any tech development that attempted to use serial designs.
