In my opinion, no, it's not the same.
The coupon books have already been paid for. Their resale and subsequent use has no effect on the cruise company's bottom line; in fact it actually would increase the bottom line since it requires the new owner to make an outlay of money to take advantage of the coupon.
Internet use involves an expense to the company; a person or persons other than the owner using the card results in additional expense to the company from a fraudulent activity.
To me it seems similar to people using other people's soda cards.