I don’t (yet) want to get into an argument about the merits of XML, or whether servers serve it properly or whether IE will (ever) understand it properly. But I would like to propose the following reasons for dropping the non-xml style of syntax:
1. Many simple coding editors rely on XML syntax to determine how to respond to opening tags. If it is not self-closing, close it later. To allow non-XML syntax would make this impossible without a knowledge of HTML5 vocabulary. This is particularly awkward while the specifications are in development.
2. XML is a useful source or intermediate format for data. Transforming this data to XHTML is a simple task. Transforming this to HTML which is not well-formed (XML) would make this more tricky.
Neither of these arguments prevents me from using the XML serialization, but that has its own problems. Given the current state of disarray with IE not handling XHTML properly, and servers not normally serving properly as a result, it would be far simpler to simply service it as text/html where the XML requirements have also been met. There is no technical reason, as far as I can tell, why a document with XML syntax need actually be served as such; after all, HTML4 is nearly that anyway ...
3. Parsing XHTML is very easy with existing XML tools which have no knowledge of the specs. Allowing non-XML syntax to become (remain?) the norm would take the cause back many years.
Hand coding in XHTML is not more arduous than in HTML, and most editors already produce the correct code.
Is this view shared? Or have I missed something, and there is something else to be gained?
Thanks