There's nothing new about book design and it's probably been going on for as long as the written word became popular.
There are still numerous traditional books around these days which show the designs were really well thought out as they have fared well against the rigors of time. If you want to get the information about books design then you can look for:
Overtime when folks became more literate, so the demand for books began to grow. As literacy evolved among the masses, the design of books had to take on a whole new approach. Book designers now had to compete and start to concentrate on a more important feature than simple page protection. It was time to design books to sell.
If you look at the book designs of today, they are nothing less than commercial packaging for a product. Don't get me wrong, book design is important because many of us not only read out books but have them on display too, which means they have to be pleasing covers. Good book designs sell books period. When browsing around a book store, the publishers are all too aware that you never get a second chance to make that first impression and with so many books on display, you need to stand out.
Clever book design also caters for the potential of a diverse readership and so a single book may have different covers which may target for say cultural sensibilities, the religious consumer, and perhaps translated versions of the book in question.