http://www.theguardian.com/media/media-blog/2014/may/18/publisher-future-magazines-content-advertising
Advertisers want to sleep with you but also want you to remain a virgin. They want to believe the favours they were granted are not being extended to the next hobbledehoy who comes along. They believe in the division of church and state as long as they can set up their stall at the altar. They talk about how important it is to maintain the credibility of the brand, while quietly hoping the brand will lower its standards just this once to let them have their evil way. If they're the only ones paying they'll get their way.