I think number of sales is not anywhere as important as the percentage of total profits, and Apple has an overwhelming dominance in that area. The reason I say profits is more important is because you end up with more money to allocate to R&D and innovate more. In addition, the bigger your war chest is, the better of a position you are to jump on opportunities that come up.

Perhaps this is why Apple managed to come out with two revolutionary products (iPhone and iPad) within the span of just one decade, whereas competitors are mostly stuck in reactive mode.