I would hope that the number of people that don't tip the recommended amount are very few. I like the idea of the up-front tipping, I don't believe that the service will deteriorate because of it. This would insure the Cabin Steward and Waiters will get paid for the services they provide. You can always change it, + or -, depending on the quality of service you received. I've been on 5 cruises and have nothing but praise for these hard working people. Remember that they deal with many "types" of people, this can't be easy.
I have seen people not show up for the last dinner or breakfast to avoid paying the tip. Talk about no class. I've always had great service when cruising and over tip to show my respect. You get all types out there.