True, because it's based on their spyware-toolbar, so you only measure the people who are relatively clueless about their computer - but in absence of the 9gag-people citing their sources there's not much more to do.
I don't know how ranking.com generates the numbers, but in their ranking reddit.com is 11,763, 9gag is 11,768 and 4chan is 11,775 - all kinda identical.
Actually, 9gag does release their numbers, via Quantcast[0]. According to those, they have a long ways to catch up to Reddit, which even in 2010 [1] had more than double the visitors (3mm vs 8mm "people" monthly).
Incidentally, the 65mm visitors from that quote seems to have been actually referring to page views, of which Reddit had 429mm monthly in 2010.
