"I'm curious: why hasn't some infuriated iPhone developer thrown the relevant amendment (first?) of the US constitution at Apple claiming censorship?"
Because it's not censorship. Only a government can be a censor. The Sun is still available to anyone who wishes to ... err ... read Page 3.
On the other hand, I won't purchase anything from a company that thinks it can decide what I am allowed to do. I am an adult, as is anyone capable of entering into a contract (by law). It's not up to Apple (or any other company!) to decide what my daughter might be allowed to do. Rather, as her parents, it's my Wife & I's job. Or was, she's over 18 now. Thank gawd/ess :-)
On the gripping hand, when the Wife's iPhone contract expires, we're not renewing it. It'll go into the box on the top shelf of the office closet, joining the dozen or so other phones that she's tried over the years. Eyecandy does not equate to usability or usefulness. Our day-to-day phones are nearly 10 year old Nokea 5185s ... Nothing has even come close in usability & durability, to say nothing of battery life.