There's actually been plenty of tech industry people suggest/speculate (with previous products...namely iPhones) that Apple themselves creates an artificial shortage of products, meaning they have plenty of the product, yet trickle them out, just to create the "sold out/must have product" buzz, which is worth more than any amount of advertising they could do. Just Google "Apple creating iPhone shortage" and read at some of the industry and tech experts that have suggested that Apple does it on purpose. Normally, your theory of "losing money on product that sits on shelves" would hold true, but Apple has a unique position over the past few years. Instead of a shortage being a possible sales risk, Apple has turned it into any "shortages" into a positive sales tool. The normal risk would be that a customer that goes wanting an Apple device and finding it not available, might buy a competitor's product instead (this is a real threat to "out of stock" scenarios for most manufacturers). But with Apple, and the way all of their products have become the "must have" products in recent years, people actually try HARDER to get the devices when they are out of stock. They camp out, they line up all freaking day, go to excessive lengths just to get the iDevices. It does "hurt" Apple in the slightest to have these shortages...just look at all the free press/buzz generated by them. All it does is seem to drive the Apple fans into even more of a frenzy to get the products.
