Could you actually describe this? How would that be a better analogy?
As a vehicle owner I'd like to be able to have a choice whether I want to install OEM parts or after market parts. The after market parts might be cheaper, or have features that the OEM parts lack. I would like to be able to purchase these parts without a 30% markup that goes to the car manufacturer.
As an iPhone user, I'd like to be able to install apps on my iPhone without having to pay the iPhone manufacturer a 30% markup.
I realize that this analogy doesn't directly address the issue of whether Apple has a monopoly on the market of iPhone apps, but it's how I think about it as a consumer.