As micks56 said below, this has everything to do with how the combination of Apple selling product for enough profit to be able to do things like pay advance cash to their suppliers. This pushes almost all the inventory (material & finished goods) off their books entirely, and by enabling things like direct ship by Foxconn they basically then only have to semi-accurately forecast demand at their retail stores and minimally ship to stock for the shelves and small warehouses that support them.

This doesn't belittle Apple's achievements at all, but considering they only have ~20 component suppliers and 1 integration partner, it's a pretty damned simple supply chain.