Doesn't surprise me at all. Generationally you are talking about people who were young in the "free love" 60's and 70's against people brought up with the threat of AIDS during their teens. It's obvious whose more likely to wander off really.
We have become increasingly sexually represed over the last 40 years, so I think the findings will be absolutely accurate, as the over 50's certainly won't feel they need to have anyone else's permission to sleep with whomsoever they please, wheras younger people have been brought up in far less promiscuous circumstances.