That doesn't make any sense. Canvas is a standard maintained as part of HTML5 by the W3C. How are they "not really using HTML5"? Just because they don't have some tags? That makes no sense. The web is not HTML and CSS. People need to get over that.

As for semantics and stuff, this isn't designed for documents at all, which HTML is perfectly suited for. This is designed for native-style applications in the browser where semantics don't really mean anything anyway. And like I said in my article, accessibility is taken care of.