In reply to AJ.

What do you mean, it's right in the article?

> "All the subdomains of http://wordpress.com and http://wordpress.org do indeed only count as one site. Sites that are hosted by Automattic under their own domain do count if they have significant traffic on that domain. These are 0.4%, 29.5% are hosted somewhere else."

In short, none of the foo.wordpress.com sites count towards this metric and the only .com sites that do have a custom domain (and the wp.com sites with custom domains are 0.4% of the total).