The study in question had nothing to do with how many men have seen porn, despite the title of this thread.
They were attempting to study whether porn had any effect on men's sexuality, attitudes to women, etc. Which is why the study was on men - there isn't anyone stridently declaring that watching porn turns women into murdering rapists who hate men, yadda yadda.
Surprise, surprise, the study had the same results as all the others doing the same thing: it doesn't. Men who watch porn don't "progress" through ever more abusive porn until they can only get aroused by snuff movies (that are on sale everywhere in the anti-porn feminist fantasy view of the world). In reality, men (and women) choose porn that suits their tastes and generally continue to seek that same type of porn, because it suits their tastes. Porn might uncover a taste for something, but doesn't cause it. For example, someone might see a golden showers clip and find it exciting, but if they don't find it exciting, they won't go looking for more golden showers porn and they won't find golden showers porn exciting just because they've seen it. It's not a surprising finding, really.