Assuming that internet connections are usually available ensures that your device will be utterly useless in many rural areas. In some places around my city, there is no broadband internet available at all, perhaps even when considering offerings from cell phone networks.
There is one place in our city that offers free wifi, and few people are aware of it because they do not advertise it. Our library has computers one can use, but no wifi.
People living in and around major cities may want to pretend that everyone is able to have nearly continuous internet access, but that's not the case. Even assuming one has a smartphone, Edge isn't a pleasant thing to attempt to even browse the internet over.
The analogy is not perfect, since you can buy mp3s and movies and ebooks from other services. But on iPhones and iPads the barriers to getting content from non-iTunes sources is certainly higher than it otherwise would be on a regular Mac (or any other PC for that matter).