#Amazon barely gives any discount on some books, compared to their child company BookDepository. Seems to me this happens mostly on titles with a smaller audience (e.g. Peter Watts).
On those cases, the Kindle book is about 50%-60% of the price, whereas in others it's common to see Kindle books that are almost the same price as the printed book.
Wouldn't surprise me if they're pushing to go #Kindle-only for anything that is not mass-market.