As the meme goes, "that's a nice hypothesis you've got there. Be a shame if someone were to test it". If tipping fixes a supposed incentive problem that exists with tip-free service, than restaurant service should be better in North America than anywhere else in the world. Is it? Empirically, no. And even locally there is no gain from tipping: Seattle has several tip-free restaurants and the service is indistinguishable from the rest of them.