Supply and demand... supply and demand.
Hard to predict supply on a first generation product. Now that they have hard data on what people are buying, they're adjusting their production.
It really is literally impossible to predict. And from what I remember when I visited Apple a few years back on business, they don't conduct any user studies ahead of time that some other companies do that can sometimes yield this information.
Once this irons out, it'll be smooth sailing, most likely for the 2nd generation as well.