One of the concepts I came up with early in my days at LibreDigital was that discovery for electronic items, especially content on publisher websites, demanded a different sequence than traditional print sales. Yes, everyone was working hard to implement several digital analogies to the print experience, the Look-Inside program at Amazon probably the most well known (but substantially behind the tools we had at NewsStand/LibreDigital at the time for BrowseInside.)
The assertion then, and the one I continue to make with our publishing clients is this: a user on your website should be making first a content use (or value) decision, then a format decision. It was the separation of the two (at the time) that was new. Most publishers (then and now) separate Books from eBooks as "types" on their websites. This concept and its implementation has major impact on the choices of layout on a website, usually right at the primary navigation level.
Taking basic principles of selling websites, separating the format decision early is likely to lead to a higher percentage of lost users - especially if the eBook set is not complete.
We propose that the publisher website be designed to help the user decide if a specific piece of content will likely solve the need (be it amusement, knowledge, etc). Once the person has clearly made that choice, then and only then, present the available formats and enable the choice.
Not only does this make the format decision secondary (the person has already decided the content is valuable at some level or would not have moved forward), but it sets the publisher up for enhanced eBooks (and the supportive pricing models for same, but that is a topic for another article)...