OP: your post is spot on, including with the estimates. The things that you list under outstanding service are the true differentiators: a cherry on an order of ice cream may be seen as superfluous by many ("I just wanted ice cream!"), yet has a huge impact on the experience and differentiates a "nice" restaurant from an "average" one.

If they could get rid of the bottom 5% the perception of the average service would improve dramatically; a bad experience can be 6x more powerful than a "normal" one.