Comment by NateyJay

The PWM backlight driver frequency should be much higher. This kind of effect is only perceptible at sub-kilohertz LED switching. The LEDs themselves are happy to be cycled into the megahertz, so the only reason for this on the Macbook is poor electronic design. A low frequency does provide reduced cost, slightly higher efficiency, and reduced auditory/RF noise emissions, but visual effect has to be top priority.