Frank,
I would explain: "In some circumstances, a PA or NP can be just as good. There are other times where the difference can be critical. There are times when a lunch at your local sandwich shop is just fine. On the other hand, there are times where you want to eat a meal like the one we were kind enough to have just served you, and I would imagine that you can see the difference."
In the spirit of Christmas, invite him back for dinner next year, but instead of 100 year old Gran Marnier, serve lukewarm diet Coke. If he has the nerve to complain, explain that in some cases it is "just as good".
JBS - the typically reasoned, urbane approach. Notice that JBS is in for the long-game; he is willing to wait a year to let that diet Coke to sit and get warm & flat.
