Modules are priced individually with a sliding scale designed to reduce price as more modules are adopted. This allows instructors to use them as supplementary material or as text substitutes. Since students buy only the modules they need, they do not have to pay for a full textbook and use only a part of it. This is particularly important for quarter schools which typically cover 10-11 chapters out of a 24 chapter textbook. Also, using modules removes the constraint of having to use the same textbook for two semesters or quarters.
Most publishers offer custom publishing services.
You can order a custom pack that includes chapters from other books and combine them with the modules. See the sample course outlines section under this homepage to see how instructors have combined the modules with custom published packs. There is not enough time. We believe that instructors should ration scarce class time in a course by choosing topics that are relevant and not necessarily traditional for their students. For example, in a world in which organizational survival depends on maintaining high quality, it is more relevant to teach students how to account for quality costs in a way which enables managers to eliminate these costs and not how to account for them in inventory.