In this sentence, "I have to call my wife Diane," I believe that no comma whatsoever should precede "Diane." You're letting someone know that you are calling your wife, and her name is "Diane." But the rules say to write it this way, to show that you have only one wife: I have to call my wife, Diane. This looks as though you're telling Diane that you have to call your wife. But with the nonrestrictive-appositive rule, it mandates that we insert a comma before "Diane" to show that the speaker has only one wife. Which way would you write this sentence—with or without the comma?
"I have to call my wife Diane" = "I have to refer to my wife as Diane." However, I would still write it without a comma. Actually, I would just choose one over the other. If I am telling this to someone who knows Diane is my wife, then I say "I have to call Diane." Otherwise, I say "I have to call my wife." I realize that does not answer the question about grammar, but it is an example of how we can sidestep these grammatical issues altogether while improving the writing at the same time.
