Those are the voltage limits for power supplies plugged into the barrel jack. That goes through the voltage regulator, where there is some dropout in generating the 5V operating voltage.
The Apple adapter, on the other hand, will be providing regulated 5V through the USB port. This bypasses the arduino's voltage regulator, and the 5V is used directly. It's the same as powering the arduino by plugging it into a computer's USB port - those also provide 5V.