It's funny to think about but that is what we have to do currently if we want the same book in two different formats. It has always has been the case, and we never really questioned it because just say you bought a hardcover copy of The Grapes of Wrath, but years later wanted to re-read it while on vacation. You might very well buy a copy of the paperback, so you don't get your nice hardback all soggy when you fall into the pool while reading it on an air mattress. You had two copies, and because someone had to print them, ship them, and stock them, you paid for both of them.
Now, what about digital books? You bought the hardcover, should you pay if you want to have a digital copy as well?
This exact debate has been flaring up again and again in publishing and reading circles for the past several months (years?) but really got going when the New York Times journalist Randy Cohen wrote in his Ethicist column that downloading a pirated copy of a book you already purchased new is pretty much O.K.
Scalzi does go on to, correctly, explain that there are limits to this; and that an Audio book is different in that the reader and sound editors are entitled to their share, and obviously you can't download the Kite Runner movie just because you bought the book, but in general both of these gentleman bring up the interesting point that a digital copy of a book you legally bought is essentially the same as making a cassette tape copy of that The Who - Live At Leeds record you wanted to preserve from the ware you knew you were going to inflict on it by playing it 3000 times.
So you know how I feel, tell me know your position while we wait for the lawyers to tell how this will end.