Yes and no - Context and semantics are important
There at least two factors that are needed to make a convincing argument - two factors it seems that most here have failed to realize or use: context and semantics. The idea that Apple only allows apps to be accessed through their own store (and consequently make profits off others work) is in fact a monopolization within the context of Apple products. To introduce the argument that, to buy another company's platform nulls the monopoly, is a strawman - a logical phallicy. We are not talking about the right to purchase another platform. We are talking about Apple's choice to only allow their apps to be sold through their store. In this context the answer is obviously yes, it is monopolizing their distribution. But like most things in law, a monopoly can be a little tricky. That is why we have juries. But what is going on here is that people are arguing two different things over two different meanings of the word monopoly- the laws meaning and the figurative meaning. That being said, I believe one can make an argument that Apple is indeed breaking monopoly laws. To make an analogy, think of a car company. What would you think about a car company who made it policy that all parts for that car must be sold through them and no part can be made or manufactured for use unless first approved and sold by them...for profit. Ridiculous right? Furthermore, buying another car wouldn't null the monopoly that this company has over the availability of its parts nor would it reverse the the fact that this policy stifles the ability of other companies, who build parts, to make its own separate profits detached from the car company. And why should a manufacturer of a car also take profits from an entirely different company who is in the business of making parts for many models of cars. Its absurd. And so is Apples's monopoly of their iOS platform.