Jenna, Mike, I have a possible answer. It has to do with how chain bookstores stock books.
When brand-new books come out, there's a certain period of time they have on the shelves to prove their ongoing selling capability before they're stripped/returned to make room for other books. See, multiple copies of new books usually come to the store when the book is released, and so you'll have, say, three or four copies faced out on the shelf. Once a book is no longer new, if it's been selling well, it will go onto a "permanent stock" list, with automatic reorder when the store's stock level of that book falls below a certain number (for most books, that's one copy; for The Hobbit or something like that, it might be two or three). If the book hasn't sold well enough to justify taking up shelf space on an ongoing basis, it will be removed and stripped or returned. So you get about a three-month grace period to show that your book is worth keeping in-stock permanently--or not.
