Yes, I am aware of validation errors. These vary depending on which doctype you run it thru. The majority fall into it complaining about legacy table attributes, use of short tags which are just self closing tags and are valid HTML5, the use of the data node which is valid HTML5, and a bunch generated by Google for their maps. The biggest no, no is that <p> tag which I should fix.
Really, the important thing is that everything displays properly across the various browsers. I use to spends hours on end making sure this was perfect to a tee only to have layouts break when used within the many thousands of themes in use. Most of the CSS and tables attributes were added only to ensure proper display in as many themes as possible while providing the broadest support for browsers as possible.