My guess is that the automatic system kind of "ensures" that the staff won't get stiffed on the last night. Folks who do not show up in the dining roon on the last night and who hide from the room stewart.
If you want to reduce your tips, you have to make a concerted effort to do so.
The other thing is that the tips are now pooled and divided up by the staff. I don't know if this is a good idea or not. You can build a case both ways.
SS Norway (12 times) '85 - '97; Radiance OS 06/01; Island Princess 11/04, Grand Princess 11/04/05, Golden Princess 7/21/06, Golden Princess 2/24/07, Explorer of the Seas 12/23/07, Island Princess 11/15/08