If it's a book published by the top 6 U.S. publishers, Barnes and Noble (or any retailer) can not lower the ebook price, since the price is set by the publisher. You can Google "Agency pricing" for ebooks to learn more. Retailers can still discount hardcover and paperback books however they want, though. For example, since the paperback version is out, they may be trying to get rid of an overstock of the hardcover and so have lowered the price for that version.
What jaquellae said. That title is from one of the 'Big 6' (St. Martins/Macmillan), so the publisher sets the price of the e-book while the retailer sets the price of the printed books.
The hardcover of that title is listed as a remainder (overstock). E-books never get over-stocked, so they never go on clearance.
The publishers are finding that, overall, consumers are willing to pay premium prices for e-books, so they're pricing them higher. Among the 'Big 6', $9.99 seems to be the current bottom price for most titles.