The limitations of XPath and navigation for XML database processing

Another thread here reminded of about Michael David's recent article:

Michael discussed "flaws in the implementation of XML support for modern
databases. He explores limitations imposed by single-leg, linear hierarchical
processing, an approach used with XPath navigation of document content. He
discusses global views, multi-leg queries and using hierarchical semantics to
increase data value."

From http://www.SQLSummit.com/Articles/Navigation.htm

"This has prevented XML database processing from progressing in the way it
should have by now for getting the most value out of complete hierarchical
structures by allowing non technical database users to process them fully and
easily.

    The cause of this problem is the continued exclusive use of procedural 
(user)
    navigation for database processing,  mostly using XPath. "