Apple has a Minimum Advertised Price for all their products, just like Bose and Oakley. If you want to be an authorized Apple reseller, you need to adhere to it. They frequently allow retailers to sell below MAP prior to introducing a new revision of a product.

Lots of electronic companies have MAPs, which is why you'll see those "price too low to display. Add to your cart" notices on Amazon, Best Buy, etc.