The whole thread gives an international perspective to current debates over the censorship of violent games. While sexual content in games can be treated as pornography, the lack of existing US legislation covering violence across other media means that singling games out is plain unfair. In the UK, however, ratings of violent and extremely realistic games fall under the Video Recordings Act, which covers any recorded video media.
We have to wonder when games will get a category of their own and stand alongside more established media such as film and TV. In the meantime, to find out more about international game classification, Wikipedia's a great place to begin.