I'm late to this party but after reading the 6 pages of discussion, thought I'd add my two cents. We've been cruising for decades and the issue of tipping, additional tipping or even not tipping has been around for as long a I can remember. In the beginning it was relatively simple, "suggested" tips were to be made to the Room Steward, Waiter (Bus Boy taken care of by waiter) and anyone who interacted with you that made your vacation special. Although there were no chat boards or internet back then, you could see the main dining a lot less crowded on the last night by those who obviously didn't want to tip. Eventually the cruise lines allowed you to charge your tips to your account and provided envelopes with vouchers to hand to the Waiters and room stewards.
If this had continued it would have been fine, but what was once optional became an automatic daily service charge all under the guise of "tips" and no longer just for the waiter and room steward but for almost every conceivable worker on the ship making the daily service charge seem small to the point lots of us tip "extra". Additionally, the cruise lines are very secretive to exactly how this service charge is distributed. I've heard everything from all of it goes to the crew as additional salary to it pays for some amenities in the crew quarters with a portion paid out in cash based on performance.
This pooling of tips that I have no accountability as to how its distributed does not sit well with me. I don't believe in tipping the laundry saff or janitor sweeping the floors or anyone else behind the scenes as I don't do it in hotels or restaurents or anyplace else. I might feel different if I knew how the $16 was split but the Cruise industry does not provide that info which in itself tells me a lot.
Even after having said all that we leave the daily service charge intact and often tip extra to the room steward, waiter and busboy. That doesnt mean we wouldn'y remove the daily service charge for repeated bad performance if we felt it necessary on a rare occassion.
That's just us, there's no right or wrong and if you want to leave extra that's great but it does not mean those that don't are bad or should be shamed because they don't.