Now that I have the attention of UK librarians, this might be a good place to ask a question that has been bugging me a long time.

I notice that paperback books published in the UK usually (maybe always?) have a notice printed on the copyright page that says something like, "This book is sold on the condition that it not be resold in any binding other than its original binding . . ." Sometimes this notice is prefixed with the phrase, "Except in the United States . . ." Books published in the US have nothing like this. Yet I have never seen any wholesale rebinding and reselling of books, probably because it would be uneconomical to do so.

As far as I know, rebinding of books is an expensive process that is never undertaken except when replacement copies are very rare or unobtainable, and in that case, I can't imagine why a publisher would object.

So why is this notice deemed necessary in the UK and not in the US?