The doctype is HTML (i.e. HTML5), so it's not XHTML.

In HTML5, the closing / is optional (allowed mostly for backwards compatibility with XHTML):
http://stackoverflow.com/questions/4693939/self-closing-tags-void-elements-in-html5
http://www.reddit.com/r/web_design/comments/uvvxg/html5_developers_do_you_self_close_your_tags_or/

This cleanup was just in the process of locating the actual error, which was the missing quotation mark in the nav bar, that was throwing IE off. Not trying to get everything to validate yet.