The books bought to impress were also bound to match each other. Thus one could tell at a glance if the contents of a rich person's fancy library were simply decor accessories. On the other hand, it's my understanding that in France, and maybe elsewhere, paperback books originated as editions meant to be bound to the owner's taste. Thus they might have read those books after choosing them specifically.
Interior designers still use books as decoration, by the way, and the books tend to be really bizarre choices since they are bought by the box or yard or color or whatever. Looking for an obscure hardcover book from the 20th century? Try a design showroom.