I deleted what I posted earlier, because it was just annoying and confusing and I don't really care. I appreciate it when people supply actual evidence for their assertions.
The commenter's approach was to list only those things already out in mmpb. But he screwed up; _By Heresies Distressed_ may be listed with a paperback price to order, but its release date will be in March. Some of the other items had _very_ recent release dates to paperback (like, a couple days before he posted), so I'd be inclined to cut Macmillan a little bit of slack there, altho not much.
Another commenter notes that _Falling Stars_ by Michael Flynn came out in paper long ago, but _fails_ to take into consideration that the paperback is looooonnnng out of print (altho available enough to have almost two dozen used copies for sale on Amazon, including a "very good" from Powell's, who I would certainly trust as a seller, for $4.50. It _should_ be cheap still in ebook format. However, there is an interesting set of questions: once a book is out of print in the no-more-new-paper-copies-available, what should the price of an ebook be? And once you have digital rights, is there a reversion-to-the-author clause or is it in perpetuity?