I’ve already mentioned Apple’s insane censorship before, but I’ll mention it again.
It seems to me that Steve Jobs wants to be the moral police of the app store, not allowing anything remotely titillating (unless it’s from major, reputable sources that make Apple a lot of money, of course) on the iPhone.
To his credit, he did suggest going to Android to view porn on a phone, but still.
The thing is, there’s parental controls on the iPhone. So, use them to lock the porn away from those who you don’t want to see it – don’t block porn altogether.