This masquerading that book publishers partake of is aggravating for a few reasons. It assumes that size matters and readers won't buy books that are not novels. This assumption leads to all sorts of smoke-and-mirrors tactics with font, point size, leading, and white space -- as publishers strive for that seemingly all-important 200-page length. They will also include unwanted introductory material and criticism; or they will publish several shorter pieces together. Meanwhile, publishers will compress long novels (especially classic novels) into as little paper as possible. Therefore, at a glance it will appear that Charlotte Bronte's Jane Eyre and its 1966 prequel Wide Sargasso Sea by Jean Rhys are more or less the same length. I understand that publishers are not capricious in their marketing strategies and that these practices are based on researching market trends, but it is still an aggravation for book lovers and would-be book buyers.
