There are several benefits of using XML for content managment instead of HTML. Here is some evidence that this is catching on.
“Although XML commonly supports effective data exchange, using it to manage Web content is less understood, researchers said. But XML, which describes the content and is more flexible than HTML, can dramatically improve workflow and reduce time, effort and costs related to Web site management, they added.”
The first time I heard this idea was in 1999 in a book Building Websites with XML written by Michael Flloyd. It was a great idea but the state of the tools and the performance of XML was nowhere near the desirable level.
Today the story is very different. The tools and technologies are more mature. Techniques like AJAX on the client side and syndication formats like RSS, NewsML, Atom make it really easy to build websites with dynamic content.