Imagine that you have a publisher who tells you that, due to the availability of print-on-demand, your book will never be out of print. Great, right?
Not so fast!
Normally, when a book's sales slow down a lot, the publishers allow it to go out of print. The author gets to buy the remaining copies at a low price and the rights revert to him or her...meaning that you, the author, can take the book to another publisher who might be interested in slapping a new cover on it, or marketing it in a different way, and relaunching it. Or you may decide to update the book, maybe add new content, and go out into the marketplace with it once more.
Now consider the alternative that is proposed by publishers Simon & Schuster--and that has the Authors Guild up in arms. S & S says that as long as anybody can get a copy of a book via print-on-demand it's in print Even if years go by and nobody orders it. The upshot: you don't ever get back the rights to your book.
Other publishers have set a minimum number of print-on-demand orders that have to come in per year for the book to be considered still in print. That seems like a fair solution...we'll see whether Simon & Schuster can be won over to that point of view.