The Booksquare blog comes through again with this great post on why some "can't-miss-hits" become big flops. Blogger Kassia Krozser's example is a book for moms that she feels is better delivered as a blog than a book (more on that point in a moment). Kassia goes on to distinguish niches from trends by saying "By way of example: moms arguably comprise a massive portion of the reading audience, while so-called “Mommy books” comprise a small portion of the book-buying audience."
Great point, and any publisher who tells you they've never fallen into this trap is lying! I'll give you an example from the technology publishing world: Books on antivirus solutions. Everyone knows they should be running antivirus software on their computer. In fact, most do, but who really wants to go out and spend even $10 on a book telling you why/how to do it? The unfortunate reality is that nobody cares about the subject of antivirus until their computer gets infected -- at that point, they're much more likely to look for immediate online/neighbor solutions than run out to a bookstore.
To Kassia's point, the audience of potential customers is huge but what percentage of those people are really going to buy a book on it? (Full disclosure: My group recently co-published Simple Computer Security with CA. The product includes a special version of the CA Internet Security Suite, all for $24.99; we figured we'd try a new angle with this market by basically distributing the software itself and wrapping a small book around it. Only time will tell whether we really found a new approach or are still kidding ourselves.)
The question I've sometimes asked when new titles are pitched at an ed board meeting is, "do customers really want a book on this topic or would a nice magazine article suffice?" As Kassia accurately alludes to, I need to get more in the habit of asking whether a blog, wiki or other online resource is the better delivery mechanism for this book's content, not just a magazine...