Could this format be designed to satisfy some local expectations as to the look and feel of a "quality" book?

It’s not "some" books get one and others get the other. All books get out in a first format decided by the publisher. There’s no "default" format; it can be big or small depending on the author/publisher’s choice. Then, later, you have reprints, which are often (but not always) in a cheaper format, the one we call "livre de poche" and which sells for less money. But this reduced price has little to do with the format; paper doesn’t account much in what you pay for a book. When you do reprints you have reduced costs everywhere because the text is already there: no need for a translator, reviewers, etc; also, there’s no marketing and the author’s fees are usually lower. In fact, in Italy, reprints are cheaper even if they are usually printed in the same format as the first edition.