I’m not sure why I haven’t thought about this before, but now the reason why Apple has been banning “arousing” apps looks so clear to me: iAd.
A while ago I was talking with Peter Martinez, co-founder of Pikchur, and he was explaining to me why they have to make sure to filter out all pictures with adult or questionable content. Even if these images were driving huge amount of traffic to the website, it was driving away higher CPM networks and advertisers that have policies against advertising on sites with questionable content.
This is exactly the reason why Apple went back on his steps and banned from the iTunes App Store all the bikini/boobs/too-much-skin applications. And this is confirmed by another fact: Apple started banning those applications one and a half months after they acquired Quattro Wireless. Doing so at that time they made sure that the mainstream audience (not nerds, the only ones who care about changes in the 3.3.1 of the TOS) would focus of what the last event introduced and not what Apple banned.
A lot of people often complain about Apple’s decisions, when they ban applications or other things. My guess is that those people probably forgot that they are a business, and 99.9% of their decisions are business driven.