There is no obvious reason this product isn't going to sell in huge quantities. Less conceptually fragile, less expensive, more portable, same software stack, same media stack, same OS, same UX, same premium experience, same monstrous manufacturing and distribution reach, same monstrous advertising and product awareness engine. Every single one of the children you see in restaurants working an iPad so mommy and daddy…
Psychologically this is interesting because Apple is pulling at a lot of strings here. They want consumers to feel good about buying the product. Not resentful it's not the thing they really wanted but couldn't afford. Part of it is almost Pavlovian. The customer pays more but in the process is rewarded in different ways. For having the taste to pick the perceived superior brand for example. It's an item coveted by others, again if only because it's perceived to be superior, and it's an item that broadcasts it's premium price tag like a badge of honor with a striking design. The customer enjoys the experience of everyone swooning over their new purchase. They like the idea thousands of people are waiting in line to get this thing they are holding in their hands right now. This is even more important in the context of giving Apple products as gifts. Buying someone the cheap but acceptable option sends one message. Buying someone the expensive and also acceptable option sends a different message.
Basically Apple cracked the code of getting people to pay more and be pretty happy about it.