I think the sentiment we see sometimes that e-books have to "cost less" than paperbacks ties into some misconceptions that are very common in our society beyond just books. Many folks operate under the mistaken assumption that something physical must therefore be substantially more valuable than something ephemeral. It actually even goes deeper than that: The errant idea that cost, itself, matters. The cost can be considered the lowest price that anyone should ever consider offering something for, but if you only charge cost you don't make any profit. Price, therefore, is not related to the cost, but rather to the value.
A good example of this is home bookkeeping software. For years Intuit would ship discs with the software only to overwrite practically the whole shebang with the first update download. Now, for many thing, people realize that the disc doesn't provide them any value - only the software itself does, and downloading the software is more efficient, less wasteful. However, that kind of change in perspective takes time to take hold broadly.