Of course the vast majority with enough interest to make this list will either be sold and be an active page or still be an active placeholder but I wouldn't rule out there being a good count of pages towards the lower end of the top million being placeholders that were eventually deemed not worth trying for anymore.
A site that is occupied by a placeholder page is a 200, as far as that "top million" database is concerned. It might as well be a working shopfront or blog.
EDIT: the article uses a list sorted by inlinks, and I guess other websites don't necessarily update broken links, but that may be less true in the modern age where we have tools and automated services to automatically warn us about dead links on our websites.
Once a particular SEO trick is understood and "deoptimized" by Google, these "sites" no longer make money, and get abandoned.