To put it simply, it is a common fact that USA passengers love to tip because they are used to this kinda culture.
Whereas when you encounter non-USA passengers like myself, we either suck it up and allow for the auto gratuities or just remove it. Like I have said in a couple of pages back, the burden of paying other people's employees shouldn't fall on the customers.
It is extremely annoying to have all these hidden $++++ upon stepping on a ship. Just add the costs to the final price instead. It's like buying a sandwich that is listed as $5 and then the cashier says, "Oh by the way it is $1 service fee, $3 tips, $2 packaging on top so the total is $11." Just put the price that as $11 then.
Wth..