Good thinking. But the fact that you don't NEED them doesn't mean that some people won't BRING them.
It would be interesting if Cruisemates would get an intern (if they have them) to go through the posts for the last year, catalog the junk--er, I mean "absolute necessities"-- that people have said they carry with them, assign weights and add it up. Sometimes I'm surprised that the ships stay afloat. I truly believe that any couple arriving at the pier with 400 pounds of luggage should be thrown off the gangway, but that's bad for public relations.
My favorite overpacking story goes back a number of years when a friend was chartering his 55-foot teak sailboat out of St. Thomas. He was having a slow period, so he invited us and our cousins to come aboard for a week at cost, just to keep the boat running. We arrived at STT airport with one small duffle each for the week. We didn't have to carry them far because he had the Zodiac on the beach behind the baggage shed, and the boat was a hundred yards out in the bay at anchor. At some point during the week, Rob told us (on a stack of Bibles) that on at least one of four of his typical charters, a couple arrived at the boat with huge hard-sided suitcases and/or footlockers. In them were long gowns, tuxedos, and, of course, duct tape. Even though he (and the charter broker he worked through at the time) sent out detailed information that this was a sailboat and not a cruise ship, apparently many passengers just couldn't fathom (sorry) the difference.