I just finished preparing a textbook analysis project for my historical methods students. I am asking them to read up on a specific topic in western civ (like say the Renaissance, the Reformation, World War One, or some other lark) and see how coverage of that subject has changed over the decades. As a result I had to round up a swath of textbooks published since the 1930s until the present. After hauling a couple of dozen tomes down to the reserve desk my back hurts. I have also come to the realization that some of my fellow practitioners of the historical arts are motivated by crass material interest.
Textbook publishing is a boondoggle and there is no reason for historians to write or publishers to print the outrageous numbers of textbooks in circulation today. Do we really need a book to go into a tenth edition? Should a title be revised even after its original authors are dead? Did we really need to update that Western Civ textbook (a book essentially about European History) to encompass the events of September 11th? The attack on the World Trade Center was and is a significant event, but has enough time passed for it to be considered a 'part of history?' The answer to these questions is an emphatic No.
There is no intellectually valid reason for a textbook to be updated more than once a decade. The only reason that there are new editions or more than three survey textbooks on Western Civ is because they are Cash Cows for publishers and authors alike. Academic publishing has very meager financial rewards. Historians do not collect royalties on their monographs or articles. The publishers don't make any money at it either. The one place where they can make a modest sum (perhaps enough to put one of their children through college) is in the textbook business. Far be it from me to take the bread out of another scholar's mouth, but for dog's sake, lets not reduce history to the intersection of frivolity and cupidity.