This is NOT a "uniquely European cultural thing" as I have experienced the chair hog issue on my last (and first) cruise in early April due to large American families. They must have taken turns on getting up early each morning to stake out the whole front section of chairs right in front of the family pool. Within the first couple of days the chair I was sitting in was taken over by someone when I got up to use the ladies room and another to get some coffee. Since my kids are teens I felt it unnecessary to subject myself to this nonsense. I hung out at the Aft pool (adults only) where chair hogs don't exist.
I travel alot in the Caribbean and find this chair hog business to exist no matter where and mostly by people who travel in big groups from the US.