Why XHTML5?
Some of the pages are software documentation and produced with the help of the “Docutils“ documentation utilities. HTML-code generated this way is also transformed into PDF-versions of the same documents with the help of the Apache-FOP XSL/FO processor.
The XHTML format is the best suited for this purpose and those pages are served as application/xhtml\+xml. Writing all my pages as XHTML5 saves me the trouble to handle alternative HTML-versions. XHTML 1.0 is anyway the HTML dialect that I have used the most in the past and XHTML5 is thus a choice of convenience – or laziness if you prefer.