It's long been a favourite device to cloak some less respectable book in the cover of a much staider one
The diligent soul on your train purporting to be engrossed in The Primary Structures of Fabrics: An Illustrated Classification may in fact be secretly savouring the sex life of Fanny Hill. The dust jacket, an institution dating from the early 19th century, is a much more precious and versatile creature than some imagine. Eyecatching covers sell books that would otherwise struggle – which is why, as Private Eye keeps pointing out, so many designs today are so hauntingly similar.
Books with their jackets intact have a far higher resale value than those without. There's a popular cliche, second only perhaps in its category to "all that glisters is not gold", which says that you can't judge a book by its cover. Sound advice at all times; but especially so in cases like this one