HTML Vs XHTML

It is well formed HTML (i.e.) obey XML schema rules and as a result it can be used with wide range of XML tools that makes XHTML a very salable and reliable document type. 

For exaple writing a XPath Finder tool for html page is lot easier it it is well formed

More References 

1. http://www.sitepoint.com/forums/showthread.php?393445-XHTML-vs-HTML-FAQ
2. http://www.diffen.com/difference/HTML_vs_XHTML
3. http://funfacter.hubpages.com/hub/5-advantages-of-XHTML-over-HTML