And, of troy, your mini lecture on pies doesn't surprise me at all!
I still wouldn't think of a pecan pie as being a custard pie, cookbooks aside. I do think of custards as having milk, as Jackie suggests--but my thinking could be absolutely incorrect and just based on limited experience. From what you wrote, I learned that pies are classified as custard and non-custard, but I've never heard of that before. And chess pies don't appear to be custards to me--although you've written that they are. So be it. My impression of 'custard' moves out a bit--but it still feels weird. A milkless custard. But I suppose that's just an instance of cognitive dissonance. A concept is strange at first, and then you just accept it--because of cookbooks. Fine.
A quiche seems easy to accept as a type of custard pie over a chess pie, however.
[tangent alert:]And we shouldn't forget Mary Poppins' observation: "Piecrust promises: Easily made and easily broken."
