Creo que si usan los dns en combinación con algún otro mecanismo, sin embargo es raro la limitación de algunos tld.
(tomado del link que posteaste)
Cita: The clients of a Web Hosting company are identified as all Domains served by the nameservers of that particular Company. This may however not be true in all cases. In certain instances the DNS provider maybe separate from the actual Hosting Company. In such a scenario, those domains will be counted towards the DNS provider and not the Hosting Company.
P.D Modificaré un poco el post original para hacer hincapie en lo relativo del valor de este test