I don't think it's just that they have fewer items in a category (they do) but that if you took all their SKUs for all products into markets, sub-markets, demographics, and ultimately individuals making purchases/using a particular SKU and organized it into a hierarchy - it would be almost a perfect tree with very few leafs touching the same branch.

Compare to Dell, whose equivalent datastructure would be a directed graph that probably contains cycles and non-sensical topology.