If it was just one cruise, then I would tend to agree with you that it's fairly insignificant. But over numerous cruises (and other instances of delaying paying for things as long as possible), it adds up.
Along the same lines, I always get a kick out of people thinking that getting an income tax refund is a good thing. In reality, it's best to owe income tax (provided that you haven't incurred a penalty, of course).