If I remember corectly they changed system to prefer pure sprinters like Cav back in 2011. One of the reason if my memory is right was that in 2009 Hushovd won one stage and Cavendish six stages in 2009 but Hushovd won Jersey. Than Sagan came and was head and shoulders above rest. Than Sagan won green without winning stage in 2014 and than oficials changed system again to favour pure sprinters with more points for win and less for placings. Sagan won in 2015 again without stage win. The system would be really skewed to allow somebody beat peak Sagan. However this year he missed something just like in the classics (but not so much) but nobody really tried to challenge him. I think this year was first time he was beatable.