It's a great question that was just posted on Linkedin by Becky Carroll who writes a terrific blog called Customers Rock.
I encourage you to read the answers and to visit Becky's blog, as she plans a deeper dive on the subject very soon. Here was my two cents:
I really enjoyed reading the answers to your very good question. They support the fact that client service excellence, just as beauty, is in the eye of the beholder. For that reason, 5-star service is more of a frame of mind aimed at the individual than a ubiquitous goal for the masses. As Frances X. Frei suggested in a recent HBR article, it's not about being all things to all people, but being specific things to specific people.