This question was asked recently because we released the paperback of a title one month before we released the e-book edition. This is a simple question for the reader but the answer is complicated for the publisher.
From the point of view of the reader, they want to have a choice, print and ebook at the same time. The fact is—the print is more difficult to put together and more expensive too. Even with POD technology, which is what we use, it costs more in monetary terms as well as time and effort.
Many traditional publishers release the hardback first so as to stimulate the sale of the hardback for a period of time (up to a year). They want to make as much money as possible on the hardback for the longest possible time before releasing the paperback followed by the ebook.
Others release them all at the same time but price the paperback and the ebook higher than the hardback until that period of time has passed and then bring down the price to the paperback level then they wait again for six months or so and then bring down the price on the ebook at the end.
What we have decided to do is the following—Release the print first at a higher price but only wait one month between formats thereby obtaining the best of all possible worlds.
We feel this properly stimulates the sale of the different formats without holding up the release of the titles too much.
We will be releasing some titles purely as an ebook as an experiment to see how they do and will adjust our strategy accordingly.