Ok, but what you're really saying is its an app rated 4+ that has a mature images option. Yes its a little awkward that the settings to turn it on are only available via a website - but so what?
Parents who buy iPodTouches for their children instead of WiiU's want the parental controls to work. When their 6 year old shows their church friends boobies on their iPodTouch, they get mad and instead buy nintendo.
I agree. My point is that from Apple's perspective they have no interest in an apps internal age restrictions system. If it says 4+ it has to be 4+ for the life of the app.