What difference does it make in terms of Apple's right to choose what they sell in their store? You're taking it as a given that the platform should be open, but that, too, is their right to decide. They are not obligated to have such a store at all. Likewise, you are not obligated to buy an iPhone.
There are direct parallels with Xbox Live Marketplace, Wii Shop, and the PlayStation Store, as even more directly in the mobile stores operated by every mobile carrier. Are these companies engadging in censorship? Some of them ::gasp:: don't even sell any dictionaries!
The point is that this kind of thing goes on all around you every day and people don't seem to mind until someone starts calling it censorship. And to what end but fury? I don't understand the purpose of moral outrage over something that is merely inconvenient.
Inconvenience can sometimes equal undesirability. I think you'll find a lot of the proponents against closed platforms have the same critiques against consoles.
I actually have the same critiques of the Playstation, XBox, Wii, and every other closed harware devices that has been deliberately limited in its functionality.
If Amazon chooses to not sell certain software I can go to the manufacturer's site and buy and install it from there.
The app store on the iPhone is the only legitimate source to make an application purchase for the entire platform. Your analogy does not hold.