And that would include, I think, the article's authors. Using DOCTYPE HTML is a non-standard DTD, they haven't specified any character encoding, and whilst they've cottoned on to the HTML entity for an opening right-angle bracket they haven't yet to the HTML entity for a closing bracket. This last isn't invalid I don't think, just stupid.
Also, check out the source for google.com for some awful, non-standards HTML:
This is the sort of markup muck that they generally spit out. So with respect to "I wonder how much HTML coding the authors do" I'd say slightly more than the google web devs.