From an Intel rep on this board around a month ago he said the reason had something to do with how the lower end chips were made, that the CPU's will run at their rated speed even if an aftermarket board/chipset tries to force it higher due to the CPU checking the speed and anything trying to run faster will be disregarded and ran at the stock speed.

Supposedly this was considered a side effect of the architecture and not the intention.

He also said the lowest end Bloomfield CPU will be around $400 so no one should worry about not being able to afford the ones you can overclock.