I remember when "Under the Dome" was selling wholesale (Hardcover) for $13 and I ended up buying it from Walmart for $6.99 - because (A) it was $3.00 less than the eBook, and (B), well, I then could, in theory, resell the book.
It's odd watching two book sellers compete with each other to sell a book at loss.
But, your comment, "Amazon would let publishers rip them off in this way - paying more for something that costs less to produce." brings to mind Scalzi's comment,
http://whatever.scalzi.com/2014/07/30/amazons-latest-volley/
"(This is where many people decide to opine that the cost of eBooks should reflect the cost of production in some way that allows them to say that whatever price point they prefer is the naturally correct one. This is where I say: You know what, if you’ve ever paid more than twenty cents for a soda at a fast food restaurant, or have ever bought bottled water at a store, then I feel perfectly justified in considering your cost of production position vis a vis publishing as entirely hypocritical. Please stop making the cost of production argument for books and apparently nothing else in your daily consumer life. I think less of you when you do.)"
Think about the software that I purchase online that costs $0.001 to deliver and I pay $595 - it costs 1/10,000th what the old version with paper books, and CDs, and nice glossy boxes.
I agree with Scalzi - the argument about "it costs less to produce" is bogus. Something should be worth whatever value it has to the person buying it intersecting with whatever price the person willing to sell it wants, plain and simple. The cost of creation is not particularly interesting.