The value is that Apple allows distribution. Distribution could be handled any number of ways for considerably less. It is only valuable (especially at 30%) because it is the only one allowed.
One might say the same thing about any retail store - that distribution of my product could be done considerably less than what that store is asking for. But the whole calculation is that the value of distributing somewhere is weighed against the opportunity cost of not distributing there.
Apple's < 20% global marketshare isn't anywhere near enough to make the assertion that customers don't have alternatives.
