My guess at what happened is that Apple contracted for a huge number of DDR2-667 SODIMMs, and got a fixed price deal on them BEFORE DDR2 prices started going insane. This gives them the ability to increase the perceived value of the machine without incurring extra cost. So lets say the RAM cost them $1 at the same time other vendors were charging $1 -- no advantage. But when the same RAM costs them $1 and other vendors are charging $1.40, then it becomes a strategic advantage to include it rather than to drop the price of the machine -- because people will look at it and say "I'm getting $1.40 worth of RAM", not $1.