This is the first time that I've seen someone in one of the articles actually come up with a proper example.
Life or Debt (Kindle) costs $9.73
Life or Debt (Paperback) costs $6.00.
The thing to notice with this example is that this is a "Bargain Price" book. As far as I can tell, that's Amazon code for "remaindered". The paperback is cheaper because it's unwanted stock that the publisher has sold off, and won't be paying any royalties to the author for them. The Kindle copies will be earning the author royalties.
And look who the author of the article is: It's the author. And the rest of the article is puffing a new book and publishing project.
Although if there are non-remaindered paper books costing more than the kindle version, it's probably the publishers fault. Or just possibly it's Amazon doing a near-loss-leader on the paper book, but not on the kindle book.
Ebooks (in the absence of things like VAT on ebooks and not pbooks) cost less than the paper books. And I mean less than the discounted Amazon price, not retail price. If they don't, something strange has happened.