Not all placeholder pages will forever stay placeholder pages though. Some may get sold, become a site, then stop being a site again. Some may not get sold, come up for renewal and be deemed unlikely to be worth trying to sell anymore (renewal is cheap for a registrar but the registry will still charge a small fee).
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.