"Ian, what 64 bit chipset uses 32 bit addressing ? That is by definition not a 64 bit chipset then, sounds very strange to me but it wouldn’t suprise me if you are correct that some do (probably Intel)."
By the logic of the chipset/motherboard manufacturers supporting stuff that customers are unlikely to use is pointless, and thus it’s unusual for motherboards to support the full address range of the CPUs they have. After all how many customers are going to have more than 2gb of memory?