You can't carry neither your TV nor your desktop on the go with you like you can with your smartphone.
And I wouldn't have a problem with that in general, except it feels dirty to claim Apple are saints for graciously allowing apps like spotify to be sold on their platform. They're already being paid for doing so through phone sales. Leveraging the monopoly they hold over the ios app store against Spotify, one of their competitors, is exactly what antitrust legislation is designed to prevent.