I feel reminded of those bonus coupons where you have to cut "points" from product packaging. Wasn't it calculated that doing that amounts to working for 7$/hour (joelonsoftware mentioned it: http://www.joelonsoftware.com/articles/CamelsandRubberDuckies.html)?

So it seems to me buying books by the chapter is so complicated that the time saved by just buying the whole book at once is almost worth as much as the savings from only buying parts of it.