You also aren't locked into iOS for all mobile app purchases. My point is that this debate is usually really about whether you do or don't want to participate in a walled garden and less about whether you want to participate in a monopoly.
Using the loaded term monopoly feels like an attempt to use emotional persuasion rather than debate on the merits. Which is a shame because I think the walled garden deserves some good criticism in a lot of ways.
The barrier to buying a game off Steam given that you own a PC/Mac is much lower than the barrier to buying an app off the App Store given that you own an iOS device (ignoring jailbreaking as usual). These sorts of barriers are characteristic of monopolies.
