I disagree.
As I understand it, in this argument, "usefulness" is defined as "is styled correctly with CSS". To this end, the author cites using `"class"="span6"` on elements, which are presentational, but not semantic.
This argument may have held more clout a few years ago, but tools like Sass have pretty much solved this problem of separation of content and presentation. Using a framework like Compass allows `"span6"`, for instance, to be expressed as a function on a semantic element, leaving your markup intact.
CSS frameworks, like Twitter Bootstrap, still stuffer from this conflation, but that's just a limitation of the tools. I make no claims to a prescriptive argument on the matter--go ahead and do whatever works--but I would be interested what the author would think about Sass, or Less.