I could be wrong but I don't think there are very many rules for blog posts, as long as they don't violate the general member conduct section on the legal section. The only thing that it could be violating would be solicitation but I would think that would be allowed in blogs.
That said, the link is to an article, so I don't know if the rules there are any more stringent. However, not just anyone can post articles so I imagine the site doesn't mind since they would have had to allow that account to even publish an article anyway.
Why are such blog entries like
Kasparov on Berlin Defense
which only have the commercial intention to advertise and sell the book, tolerated here as a "training material" to learn chess?