It was looking at the shipping confirmation emails that started this. I was switching back and forth between the 2 trying to figure out if I really had ordered 2, or if they'd sent duplicate emails, and noticed that one copy cost $20.98 (plus tax, these days), the other $17.56. Amazon does have a pre-order price guarantee, so if the lower price was the result of a change between when I ordered and when it shipped, I should have gotten the lower price for both. Contacting Amazon was called for.
It really has gotten easier from those days when there was an 800-number but it was a deep dark secret. Now it's pretty easy to find the Contact us button, and be offered the options of email, phone, or chat. I elected chat, and got connected with "Benjamin S". He really did pretty well, and generally things were pretty grammatical until this point:
Since one of the book was delivered to you with less price, please keep it as a compliment.
I'm sorry for any misunderstanding and confusions.
I think that's where the available scripting failed him...
(The reason he gave for the lower cost on one copy was that it was "a mistake from the website and shipping department".)