I don't remember exactly how it works, but sometimes they advertise it as 1000Mhz, and sometimes they advertise it as 2000Mhz. There's a multiplier in there that they decide to use sometimes when they advertise it. Both processors have the same FSB though. Someone else can deal with the specifics, but I think it works something like that.
The Venices also require less voltage, thus producing less heat.