Does NPD reveal its sources? Because I think not, and they're considered reliable. Of course I could be wrong.
Anyway, the main point of the article is probably correct but other than that, the arguments are pretty flawed. At least it seems Brett's got it.
However, what I find problematic for a site's credibility is incorrect grammar. I see "their" when there should be "they're", I see "games" when there should be "game's", and so on. It doesn't look professional, it looks amateurish. I haven't read that many articles here lately but at least a while ago I used to see those things quite often. And I'm not saying I can write better, nor that everyone should, but it doesn't look professional; that's the way you write on forums, not in articles. It's not a big issue but it's probably one of the first things you notice.