It is impossible for any 32 bit operating system to address more than 4GB of memory which is really the only draw to 64 bit instruction sets
3GB is hardly the "norm" though, if you require 2GB you're in a very small minority likewise if you require a 7900/x1900 you are in a minority
3GB is hardly the "norm" though, if you require 2GB you're in a very small minority likewise if you require a 7900/x1900 you are in a minority