As the article says it's a 'commonly held belief'. There are few rights and wrongs with the exception of the 'no-no' list. Live in the UK and do any of the stuff on there and eventually you will end up in court no matter where you host.
As for the rest it's simply a matter of nobody getting into trouble for it YET. Until tested in court nobody can say for sure that the guidelines for R18's do hold true on the Internet.