It's a way of priming people, an element of marketing. You get them in the door (or site) already committed to the purchase because they think they know the price. Then they find out the truth, but they're primed to buy your product and it's easier to sway them to the higher priced "upgrade" (which should be the base, especially in this case, as the base option is too little for many users).

This isn't unique to Apple, many (if not most) companies do the same.