"I wish that SOME of the Americans on this board could grasp the fact that the ships are not American, the ports are ( generally) not American and the staff are not American, so therefore the reasoning of " when in Rome " just doesn't make sense."
When in Rome always makes sense. You are correct that the ships aren't American, etc. So the basis for the the "When in Rome" statement isn't American-standard. Indeed, it is NOT standard practice in the United States to automatically add tips to bills, as is frequently done aboard ship. However, "When in Rome" we live with this deviation from American-standard. Seems like many non-Americans aren't willing to live with deviations from their standard practices, and instead treat their own personal preferences as sacrosanct.
Here's a American colloquialism for you: "Get over yourselves."