Markets don't devolve into "monopolies" very often. In Microsofts case, it had an operating system that provided massive economies of scale to customers. You could run it on any compatible PC and be guaranteed to be able run hundreds of leading applications. Most businesses are significantly more productive with 100% windows than 50% windows and 50% other platforms. The only reason Apple Mac OS is in corporate America is because of it's special advantages in specific uses. It's always been too expensive to equip everyone with a Mac, esp. your lowest paid order entry/support types.
Most markets don't grow economies of scale for their customers in that manner. The advantage of having all of your sales people drive Fords instead of a mix of cars is a minor one from a fleet purchase perspective. And the same advantage can be had with a fleet purchase agreement with virtually any competitor.
And Apple has the most mobile device profits.
Still, I agree: nowhere near a monopoly.