There is an extra charge in the specialty restaruants for a reason, You have your choice of premium sea food and cuts of meats, etc.
These food cost and the extra service are nominal, but the cruis lines make a profit on the combined experance they are presenting to the cruiser.
Example: Princess even charges an additional charge for lobster on top of the preminum for dining in the specialty restaruant.
When your on a ship, if you want to be pampered, it will cost you.
Passengers tend to spend more on bottles of fine wine, that's another big profit for the cruise lines.
When you combine the overall experiance and the associated cost to the cruiser, it's a money maker.
It would be your personal choice to provide an extra tip for any employees on your cruise.