4) Given this is a whole new product category, Apple had to make some very very tough guesses about how many of any particular model to make. There is almost no precedent or frame of reference that they can look to build their assumptions. Even if somehow they had managed to guess perfectly which of the dozens of combinations were going to be pre-ordered and in what quantities they still have to deal with the fact that sometimes there can be unexpected issues in the production of a product, in the supply chain that provides the materials for that product, in the quality assurance of that product, etc, etc. There are tons of variables that could have led to some combination of models not being produced in the quantities they desired. There is also the fact that some of combinations are simply more difficult to make then others (the link bracelets are brushed BY HAND). In other words, it is not shocking that some models are more difficult to get then others.
