Books are going to have a number of pages (actual pages, not numbered pages) divisible by four. Even if you add in, say, an introduction, foreward, bibliography, suggested reading, index, and whatever the hell else, your numbered pages are also likely to be divisible by four, which makes sense if you look at any of these books.
It's not really some grand conspiracy.
If you look at publishing costs, also, you'll see that there are a number of industry standards. Prices often change at 256 filled pages. There are also marks at 160 pages and 352 at a lot of companies. Many companies also have minimum and maximum widths allowable for book spines, which can also dictate the number of pages allowed.