well, no Mac user will buy a Mac with a Pentium chip in it...
seriously though, Apple needed time to get OS X x86 ready for market, and to give their developers a chance to port to the new architecture. since they're waiting anyway, they may as well wait on the latest greatest from Intel to make people take notice. Intel just has to cough gently at the processor rollout and mention that Apple has a line of laptops with the processor shipping
today and it's all worth it. besides, it seems more Apple's style to go for the latest greatest. and then to stick with it until it's long dead, insisting that it can still beat anything the competition has to offer