The same method is employed with many books where an ongoing topic is continually updated. In some cases, the changes are minimal but over the years the accumulated changes make a whole different approach being suggested from what started out. For example, job hunting books, resume guides and interviewing techniques are usually (or often) updated yearly or so. It sells better to have the Whatever Topic for 2010, 2011, 2012, 2013 so that people might buy the book each year in hopes that things have changed won't slip by them. Under those banners, I think often it is just a way to sell books rather than add any useful information; rather, describing information that is the same but given a new paint job.