Hi Chuck, as much as I’d like to think HTML5 is around the corner, it’s not a final specification and in my business the client’s are always concerned about meeting accessibility guidelines and viewing their website on many versions of browsers. You’d be surprised to know how many of my clients still use IE7, which means I have to develop for that browser version and platform. I use XHTML because it’s what the W3C supports and what in-the-know clients provide to me as their requirements. The W3C validator is still useful and the industry standard of making sure that the HTML/CSS needs which are supported by 100% of the browsers and platforms are met. Plus, it can’t hurt that all tags should be closed. See: https://www.w3.org/TR/WCAG20-TECHS/H74
Looking forward to your updates, it’s a great plugin!