Oklahoma's Pioneer Library responds:
The argument against the arbitrary number is twofold. First, replacement of books in libraries is based upon the condition of the book, not the number of times it has been checked out. It is not unusual for popular books to be checked out 100 times or more before the wear and tear of circulation takes its toll and the book has to be replaced or repaired. Second, eBooks, too, eventually wear out. The electronic file formats become obsolete in a matter of years as technology progresses and customer interests change. Remember the switch from VHS to DVD or cassette to CD?