I know I'll get my ... kicked for this comment, but anyway.

The iPhone experience is not sterile at all. It comes with a browser and there is no restriction for the websites you can open. Google ('the web is the computer') should be the ones to best understand this.

Since when is controlling the quality and security of the content at a marketplace that you operate equal to limiting people's freedoms?

If I own a grocery shop and refuse to sell someone's rotten tomatoes does it make me necessary evil? Not letting people charge 0.99$ for balloons in swimwear using your own infrastructure has nothing to do with their freedom of speech. They can always create a web page and show it to the world.