It depends on where you live.For example, in Germany, there is a small very evil thing called "book price control". It was all worked before e-books, but essentially what it does, it is that it forces book prices to a certain level and the same books, but different average requirement to have the same price. It would be illegal for a publishing house offer an ebook for less than a paperback.
Fortunately most English-speaking countries have more soft regulations of the book.
