Most books don't have complex layout. What they have is extremely high quality typography and careful attention to how the text appears on a specific page. Book designers tweak prose to avoid rivers (a series of whitespace on successive lines that happen to line up with each other), widows (the final line of a paragraph appearing on its own at the beginning of a page), orphans (the first line of a paragraph appearing on its own at the beginning of a page, or when the last line of a paragraph contains only a single word), and hyphenation.

The web, which doesn't have well-defined pages or even page sizes, precise control over typography, or designers who agonize over how the actual text appears in the context of the layout, lacks all of those. Typography is slowly getting better, but text layout algorithms are still relatively primitive.

Most books have trivial layout and typography - simple, successive paragraphs with a few very minor embellishments such as the occasional large header, page-breaks before chapters, and page numbers in the footer. Preventing widows and orphans is definitely not the norm - just browse your local library or bookshelf. I seriously doubt people worry much about rivers, too.

Books with diagrams and side-notes tend to have more complex layouts, sure - and that's most educational books. Maybe there these typography issues are given more attention, but it's pretty clear that the typical paperback has demonstrated they aren't that important to readers (which isn't a judgement, it's just the way it is), so I wouldn't be surprised if almost no books worry about these issues anymore, beyond perhaps using software which addresses them insofar as they can be automatically.