Whatever happened too CSS+XML?

A few years back I was looking at this stuff, and never understood why people 
weren't more interested in it. Basically, you should be able to server a 
DocBook document on the web without every creating XHTML.  When I consider 
the effort that has been put into creating XSLT stylesheets to generate 
XHTML, it seems the same amount of effort (or considerably less) could 
produce XML + CSS that would have as much functionality as any XHTML produced 
from the DocBook XML.
http://www.badgers-in-foil.co.uk/projects/docbook-css/
http://www.mozilla.org/newlayout/xml/#linking

Steven