1. serving xhtml content using text/html content type header is considered harmful - and this is what ez does by default (http://hixie.ch/advocacy/xhtml)

2. using the html5 doctype declaration still has every browser inlcuding old versions of IE running in standards mode

3. the "video" tag in the new html-5 video variant of the ezmedia datatype is not valid in an xhtml context anyway, but only in an html5 one

4. html5 is the future