Of course, digital copies could truly put a dent in that reasoning. However, even then there should not be a cut of revenue to the publisher if the original user discontinues use of the product (so that it's not piracy). It's like someone re-selling artwork. Presumably it's in like-new condition if it was taken care of (on in some cases, would appreciate in value even if its condition deteriorates) -- but you wouldn't hear anyone talk of paying the original artist a cut of its resale value, now would you? From what I hear, book publishers are also gearing up for a fight in this arena. They have already been breathing down the neck of used-book stores, and now e-books are adding a new twist to the debate.
Thus mathematics may be defined as the subject in which we never know what we are talking about, nor whether what we are saying is true. -- Bertrand Russell