Member Rara Avis
I would agree with Ess - service isn't just the delivery of food. Granted, one expects more, the more they pay for their meal, but regardless of whether I'm in a 5-Star restaurant or Denny's, I expect the person to provide that service to the best of their abilities. As a rule, waiters and waitresses only receive a pittance for salary... in many cases less than minimum wage. Their true take home is dependent on the level of service they provide to their customers and their customers' appreciation shown in the monetary form of a tip.
I can tell you that I, for one, am unlikely to tip more than a little (if at all) for poor or unprofessional service.
Exceptional service, however, even in a cheap diner, is apt to be rewarded well.
Grammar is part of that service - it's a professional attitude that should be seen as a necessary part of the job, rather than something one would do as "over and above."
For the initial question, I would say the query SHOULD be, "How is your meal?" It is automatically implied, by nature of the expected service, that "your" includes all the patrons at that table.