When the antitrust/monopoly ruling came down from on high Microsoft held something like 90% of the home computer market. That's a dominant position. Apple maintains a solid percentage of phones, and the tablet market is too small to notice.

There's no loophole, Apple is small enough in percentages and there's that much more choice that they can't be classed as a monopoly. Don't like it? Don't buy the product. The issue was with Windows there was only one game in town for the vast majority.