The orientation of book covers

I've only noticed that last night while looking at my bookshelf... French and english books have a different way of presenting the cover. It's kinda hard to explain. On the french ones, when the book is on a table (front cover facing up), the slice of the book is written upside down. With the english books, the slice is written the "right" way.

I don't know why it's like that, but I'd like to know. The french and english librarians must have the neck muscles developped in different ways, just by the way they are tilting their heads while looking at a bookshelf...