That is just incorrect. The vast majority of the customer facing crew do not get tipped. Those waiters working in the buffet for example. The average waiter will never earn enough money from a few tips here and there to provide him with a living wage.
Plus if course, if what you say is true, when a ship has a large percentage of European passengers on board, during the summer season in the Med for example, the crew, according to your theory, would be working for nothing, given European attitudes to tipping.
P&O UK and Aus have done away with autotips, and removed the tipping culture prevalent on other lines, so all this flag of convenience nonsense is irrelevant.