Intel has revealed to the world that the upcoming Nehalem generation of processors will only support DDR3 memory. As the memory controller is now in the CPU and the Northbridge as we knew it from Intel’s past and present will cease to exist, it won't be that easy to change the memory controller in order to support DDR2.
At this point, it looks like Nehalem will only support DDR3, but we wouldn't be surprised if Intel makes a version of Nehalem to support registered DDR3 or FBDIMMs as this is what the server market needs.
As Nehalem launches as a high-performance desktop part and a workstation/server part in Q4 2008, the DDR3 prices are likely to come down to more acceptable rates.
Currently, DDR3 just can't compete with the ultra cheap DDR2 memory and motherboard manufacturers are still making high-end X48 motherboards with DDR2 support.