I checked at random, can't remember specifics.
Look at the br tags, some were closed with a /, that is an xhtml form.
I wouldn't worry about the details. With a good editor it takes less time to convert the bulk of the markup than it does to check it.
(I remember changing a code driven web site once. Over 500 pages, with systematically bad coding. That took regular expressions to fix, but in a few hours I did what would have taken weeks with hand editing.)
Discussion about HTML and XHTML related issues.