I have a theory about the cards in the machines. it is so they can track you and your spending habits. if you dont spend big on the ship, you dont win big.
We were on a cruise once and there were 2 weddings on board. One bride with the big wedding won 1000.00 on the slots the Bride with the littlier wedding won 600.00 sounds like that was fixed to me. I think the winnings are also tracked to the type of room you book. expensive rooms, big win, cheap room, little win. Just my opinion