I believe also that most of our competitors, including Wrox, break up the page too much, with extraneous screen shots, sidebars, notes, and extra illustrations. To me, it often looks like non-textual elements are added strictly for their own sake, not to enhance the delivery of information to the reader. I think our clean page layout creates a book that is easier to read and easier to search. This would help to resolve the first problem, and it would also provide the flexibility to add more content or generate savings in weight and production. Let me say first that, compared with most technical publishers, we use pretty narrow margins.
Some publishers use big outside margins for large icons or for glosses to the text.
I think you'll find that O'Reilly presents more information on a page than any of its competitors. The next time you're in a bookstore, pick up an O'Reilly book and a competitor's book with the same thickness as our book. Go to the last page. You'll discover, I'll bet, that our book has more pages. But, as you note, our margins are wide compared to Wrox Press's margins.