Perhaps it has always been this way in non-fiction publishing, but I am noticing more and more the variance between the book page totals on various publishing and online bookselling websites. For a given title, it is not uncommon to see a different page total at every venue visited; and the differences can be quite striking. Additionally, the retail version of a particular book can often be found in reality to have far fewer pages than the publisher's 'official' total. Whether this is an intentional marketing move ("page inflation") or an unfortunate consequence of the workings of the publishing pipeline, I don't know. Perhaps publishers submit the totals to retail websites & distributors from early galleys, and final formatting, font changes, etc. cut the page total down substantially. On the other hand, I've never discovered a book in my hands to be lengthier than advertised!
Somewhat annoyed at all this, you might have noticed that I've been rather guilty of creating my own page total convention. For the reviews on this site, I take the number on the last page of the main text and add the notes and appendices to arrive at my own number. This is more of a 'reading total', and assumes that you are like me and always read the notes and appendices.
This was never made clear, but I wanted to mention the new change. From now on the convention I will use will involve two numbers "Pages: Total/Main Text".