I think people are talking about technologies without looking into the using them and even more importantly, having learners access the pages created by them.
Presently HTML is king when it comes to a language used to create web pages. I think HTML's limitations has some advantages, specifically making it accessible to more people. for example this is a an easy way for SMEs to create web courses. Actually,
HTML by itself isn't used by SME's, but authoring tools that
create it does. Then, there are other tools like Google Docs,
FrontPage, & DreamWeaver that can easily edit what the authoring tool has
created (if there is a need for that).
XML is being used more often for display of content, and that is
fine. Likewise, it is being used more frequently for data storage, and
that too is good. However, simultaneous use of an XML document for both
display and for data storage seems extremely difficult and what would
be the point of doing this?
XSLT (style sheets and display for XML) is and will be very useful for what it is intended to do. I don't know what tools actually do the XSLT translation?
For example, browsers can display HTML and XML, and different parsers
can read/parse XML. If you use an XML parser, you still have to program
the interpretation and use of the parsed data, and that is fine because
now there is a more accessible file storage format. With XSLT, what
creates the output file?