I smile when I read about the Entertainment Book coupons. In many years, here in Florida, we have never yet sold a cruise for which one of those coupons was valid. I would suggest that the problem is not with the cruise line, but rather with the publisher(s) of the Entertainment Book. Because of our proximity to the major cruise ports (we are in the "drive-in" market... where people do not have to fly or plan way ahead to cruise), we get very excellent cruise pricing as a general rule... far below, actually, the minimum rates against which these coupons can be used.
I wouldn't look a gift horse in the mouth. As I said before, what counts is the net amount one pays to embark a ship and what one gets for it. You can call it what you will... "2 for 1", coupons, "buy one get one free" or whatever.