Dear Aunt TUAW,
I'm in love with the new MacBook Pro Retina but it's way too expensive for my wallet. Why can't I just get a Retina display on an affordable MacBook Air instead?
Your loving nephew,
Although a lot of consumers would benefit from a consumer Retina display, it's not that simple both for economic and technology reasons.
The Retina display provides one of Apple's key selling points for its top-of-the-line models: the iPhone 4S, the new iPad, and the new MacBook Pro. Although the new iPad is a "consumer" machine, it represents the high end of its iOS family.
Adding the Retina to a budget Air would degrade the desirability of the new feature, allowing more people to "buy down". That's something Apple would prefer to avoid when the Retina display is so new to its laptop product line.
The laptop display is also much bigger. The iPad's 2048-by-1536 display uses just 60% of the pixels of the MacBook's 2880-by-1800 display. There's a price differential right there. Also, as Uncle Rich points out, a smartphone-class GPU is not in the same league as a mobile-computing one, so the hardware to support the larger display is more costly.
The iPad uses a fabulous battery but isn't tasked as much as a laptop battery. Its 42.5 Watt hour battery delivers almost twice the battery life as the MacBook Pro does. Adding the 15" Retina display to the MacBook Pro and keeping the battery use-life the same bumped up the 78 Watt hour MBP battery to 95 Watt hours, an 18% increase. Again, the higher battery needs must be taken into the cost equation.
If you add the price of the display, even a smaller Air-sized one, the enhanced GPU requirements, and the upgraded battery to the consumer MacBook Air, the costs would start to creep up -- perhaps not to Pro levels, but up.
Will we see a Retina Air? Auntie thinks, "yes". Will we see one very soon? Probably not.
Apple MacBook Air 13-inch (early 2015)
Apple MacBook Pro 15-inch with Retina Display (mid 2014)