Apple's App Store is the ultimate monopoly. Not only is it the only app store you can use to purchase software for your iPhone or iPad, but it's also the only way users can install new software. Yes, iPhone users can jailbreak their devices to install third-party apps, but that's a somewhat risky process that voids your warranty, and the number of jailbroken apps is relatively small. In contrast, Android has at least a dozen legitimate markets and the ability to sideload apps built right in.
Why should you care about installing apps that haven't been blessed by Apple or Google? Having freedom of choice means more selection, no arbiter banning apps it deems offensive or competitive with the company's other services and more places to shop around for the best price on paid apps. In addition, if you want to write your own app in Android and send it to friends, all you need to do is email the install file. On iOS, you can only install self-made apps with a developer's license or by putting it up for evaluation by Apple's App Store censors.
More: Best Apps 2013