Originally Posted by Kali Yuga
OK, so basically you found just about the only ebook where the paper copy is cheaper. Release the hounds, pass the torches, etcetera etcetera.
If you look a little further, you'll notice that the newer trade paper has a list of $15 and the same cover as the Kindle edition. I.e. Tor is setting the wholesale price based on the trade edition, and Amazon apparently doesn't feel like losing $3 per copy on this particular book.
BTW I find it somewhat unlikely that Tor is blinded by money and short-term profits. Although they are owned by MacMillan, and like every other for-profit company don't want to be in the red, they're a small genre publisher, and clearly more interested in selling works they like than just "whatever they think will sell."
FYI I have seen several times where a book is straight to paperback for 7.99 (as in no hardcover or trade published before) and a publisher will sell the ebook for 9.99. So it does happen. I saw the price points that the OP posted and assumed it was the same. I'm a little more lenient when a book has gone from hardcover to paperback and the ebook price doesn't reflect that, although that has gotten better in the past year.