Web pages are a giant mess of content and presentation, and CSS doesn't really help much. XML is at least a way of describing data in a meaningful way. <book>, <author>, <chapter>, etc. XSLT provided a way of formatting XML in the browser. Sure the internet would still be full of inconsistent content structures, but it would still be way easier to machine read than the big mess of arbitrary <div>s and <p>s (most of which just display something blinky) that we have today.