I agree with Steven Champeon - let's not get into the habit of allowing costly 
management strategies just because they're already employed in the impromptu 
world of HTML or the more (and less) structured world of SGML.  XML already 
has a difficult enough burden to carry as its inheritance.
I had the pleasure of working with someone who kept track of 10,000 pages and 
their dependencies in her head.  There were basic rules, but she could keep 
track of the (many) exceptions as well.  If only I could find a product that 
did nearly as good a job as she did, then maybe these issues wouldn't be so 
critical.  Until then, I'd rather not see them shrugged off.
I would _much_ rather see efforts to encourage Web developers to move to XML 
because of its ease of use than "well, it's not any worse".  XML may be 
skyrocketing in anouncements for data applications, but getting Web developers 
to use it on its supposed killer app is going to take a lot of further 
development and consideration for the needs of that application.
Simon St.Laurent
Dynamic HTML: A Primer / XML: A Primer / Cookies