As to why to go this direction ... the whole world's going this direction. HTML 4.01 is the last HTML standard W3C will put out. Everything else will be XHTML.
Until yesterday I never heard of it, but there is an upcoming HTML 5.0. http://www.w3.org/html/wg/html5/
Relationship to HTML 4.01, XHTML 1.1, DOM2 HTMLThis specification represents a new version of HTML4 and XHTML1, along with a new version of the associated DOM2 HTML API. Migration from HTML4 or XHTML1 to the format and APIs described in this specification should in most cases be straightforward, as care has been taken to ensure that backwards-compatibility is retained.
This specification will eventually supplant Web Forms 2.0 as well.
Relationship to XHTML2
XHTML2 defines a new HTML vocabulary with better features for hyperlinks, multimedia content, annotating document edits, rich metadata, declarative interactive forms, and describing the semantics of human literary works such as poems and scientific papers.
However, it lacks elements to express the semantics of many of the non-document types of content often seen on the Web. For instance, forum sites, auction sites, search engines, online shops, and the like, do not fit the document metaphor well, and are not covered by XHTML2.
This specification aims to extend HTML so that it is also suitable in these contexts.
XHTML2 and this specification use different namespaces and therefore can both be implemented in the same XML processor.
