Apple is not monopoly in the sensr of traditional definition. Apple is monopoly in its own little circle. If you want iOS powered devices, too bad, you can only buy from Apple. Consumers have little choice beside accept Apple's price.
If I want Android phone, I can choose from Samsung, HTC, Motorola, Huawei, Xiaomi and host of other manufactures. If I wanted Windows machine, I can get from Samsung, Lenovo, Acer, Dell, HP and host of other manufacturers. If I want iOS devices, I have to buy from Apple.
Apple also have control over its own products. It is good thing for Apple, becuase they can control it and maximize its profit and improve their products' usability. But it is also up to Apple to decide when to abandoning one devices and when to cripple older devices. When Apple decided to abandon one device, you will never get support from Apple. On Android side, I can still flash CM nightly for latest update.