Apple have a monopolistic control over how you sell software for their mobile devices, and Amazon have a similar monopolistic control over how you sell products on their website.
Both can only be an actual real monopoly if they had no realistic competitors. This is not the case for either Apple or Amazon.
That kind of 'monopoly' isn't what people mean by 'monopoly'.
They're thinking of things like telcos who have (or had, in some cases) government-granted monopolies that prohibit potential competitors from even trying to compete, or they're thinking of cases like Microsoft back in the day when they used their leverage from a dominant position in one market to attempt to force out competitors in a different (but related) market. (By shipping IE for free at a loss to ensure that Netscape couldn't profit from selling a browser, for example.)
That's why people deliberately incorrectly use the term when referring to Apple. They're trying to evoke that feeling of a big corporation with an unfair advantage.
But that only works if Android doesn't exist, and BlackBerry doesn't exist, and Windows Phone/Mobile doesn't exist, and Symbian doesn't exist (which will be true soon, I guess!), and WebOS doesn't exist, and something prevents competitors from even trying to have their own mobile platform.
Apple have a monopolistic control over how you sell software for their mobile devices, and Amazon have a similar monopolistic control over how you sell products on their website.
Both can only be an actual real monopoly if they had no realistic competitors. This is not the case for either Apple or Amazon.