Although the retina model is more superior in terms of performance power and visual productivity, and no one would dare to discount the clarity of the retina screen, but its still stand at this point that the retina screen is very dodgy. He will have a very high chance of getting a "bad retina screen", bad as in image retention or ghosting, than if he were to get a defective air.
The bad screen and the frustration of going back and forth to the apple store to get exchange will ruin the whole experience.
First of all, don't make any conclusions based on what you see on any forum. A disappointed customer will be much more vocal than a satisfied one.
Second, I technically have one of the bad screens. Under very specific circumstances, I can get my display to exhibit image retention. However, under normal use, I cannot see any retention, even with a gray desktop background. And even if I deliberately get retention to appear, it disappears very quickly (within a few seconds if I let the pixels refresh).
On the flip side, what the display does well, it does extremely well. The colors are the best I've seen on any laptop display. Reading text is a delight. The background is very uniform. The screen is equipped with an A-TW polarizer so the IPS glow is non-existant. It's just a very good screen overall.
So there really shouldn't be much frustration. Even a "bad" retina screen is a hundred times better than the air screen. It's just a much more satisfying experience.