I wager they don't sell many copies. Funny thing about pricing sometimes. I mentioned a book over at Smashwords "Jane's Free Guide"
http://www.smashwords.com/books/view/44057 after downloading a copy and reviewing it around feb. 25th this year and shortly thereafter it went from free to .99 for a copy so it's not just Amazon that might be doing it. Either I caught the book just after she'd uploaded it to Smashwords (and before the price was set) or the attention it got after I posted about it here got her attention. I don't know which.