Is torture better for kids than naked breasts?

I don’t get the UK ratings system.

A movie like Coming to America, which is entirely harmless but contains a few naked boobs and sexual references, is rated 15.

On the other hand, Casino Royale, which contains graphical scenes of a naked man getting his testicles whipped, is rated 12A (which means that no kid is too young if accompanied by an adult).

I think I prefer Spanish ratings for violence (Casino Royale: 18) and Swedish ones for nudity (Coming to America: 7).