Why Switch to XHTML? - WebReference.com

I haven't have a chance to take a look of a site writen in XHTML, but in this article, it seems will appear soon- Why Switch to XHTML? - WebReference.com

In the tech documents I read before, mobile OS (especially for Symbian) are often support XHTML in web browsing- I'm not sure what it looks while looking pages writen in HTML, XML or XHTML- if the output can be optimzed for both PC browsing and Mobile browsing with one time coding, that will be perfect.