As a good friend used to say "I only had one day of schoolin and that day was singin, so you'll have explain this to me real slow."

Way out here in the woods, I've only seen HS's where the top press-fit in the tube is a cone/race and the bottom is a cup. Bottom cone/race fits onto the fork crown and top cup threads onto the steerer. NO way to reverse them. But are you folks saying there are headsets where both upper and lower cups are press fit into the head tube? So the top cone is threaded onto the steerer. WHY, fear g'sake? Seems life a fine way to get water into the top bearing assembly then, inevitably, the lower.