Not a cultural thing. Some years back Bob McCoskie from Family First, and very much from godzone, complained that his 16-year old daughter had seen naked men on a fluff TV news item on naked rugby. He said he didn't know what to say to her afterwards.
I kid you not.
He needn't have worried. She has plenty of other sources. The Internet, neighbours, relatives, the stranger in the dirty mac, other girls who know even less than she does, but do know that jumping up and down prevents pregnancy.
Strange that he was at a loss for words, though. He never is when it comes to telling other people how to live. Maybe he has just never seen a penis, including his own?