The other thing about articles is that they increase credibility for your site. Often users are not aware that the person who wrote the article owns the site that is being linked to and is doing it to get traffic. In a sense, seeing your article (if it is well-written and informative) on a third-party site is taken as being a third-party recommendation. This can obviously have a knock-on effect in sales, which I have seen for myself with the site in my sig.