Where is this rule written? Do you cruise? Cash tip a favorite bar tender? Where does the cash go? Yep, right in their pockets. Same with cabin stewards, head waiters and the guy cleaning the bathroom.
Grats are for service. How could Royal possibly know better than the customer how the service was? How can you even think that thought process is valid. Do you let the restaurant owner decide who gets your tip, handing it to the owner and not the waiter?
This over used threat is really a rude comment about hard working cabin attendants. Do you really think that an employee would act so inappropriately... or just being a smarty? Additionally, your half baked theory ignores that those who remove auto grats DO tip in cash at the point of service and often tip above the auto grats. Read the threads and learn.
Op said: "I just booked a b-2-b on the Voyager today for April 6th & 9th, and my dining time was posted as Wait Listed for 6 PM." Maybe things have changed, but just saying are you sure isn't helpful.