The Myth of the Long Tail
The real question is when does having access to many products really help a business. I'd argue that for a store, money would go out the window because you couldn't get enough people physically through the doors to make money from their interest in the vast majority of items. In my own business experience, I've found that some amount of "extra" items can help a catalog appear to be the place to go for products, even though the bulk of sales still come from the normally hot items, but even then you have diminishing returns because of the cost of printing a catalog. Even in a web-only environment, there's still a cost of bandwidth, of managing a database, and of communicating with vendors to get products in. So, the long tail - in moderation - can help boost overall sales and even profit (higher margins) of resellers. If you're a vendor, though, putting your faith in what this can do for you is probably foolish ... unless you're the vendor that came out with the book in the first place.