At least they could have had a better lame excuse. Waiters aren't responsible for food quality and cabin stewards don't buy the beds. But then as you say they had no intention of tipping anyway.
I sometimes think the ship should give the non-tippers a special debarkation number so they can all leave at the same time, and then pass the word around so they can be mocked by the other passengers. Sort of a cruise version of a perp-walk. And put their luggage in a special 'non-tipper' section so the porters in the terminal ignore them.