If you use a credit card and something happens, you have the option to dispute the charges and the credit card company will help you. We've traveled all over the world and have been on 43 cruises - we've always used a credit card and have never had any problems. In all that time, I've never had them not release any holds within a day or two, but obviously stuff happens for some people. Plus, we've had thousands of clients use them and never had any problems, with the exception of one person. Chances are problems won't happen.
And I didn't say travelers checks are not accepted onboard ship - I know for a fact they are. I said they are becoming a thing of the past.
And I didn't say the bill you get in the morning will be the final, I said it should be the final, but things happen.