Is it really hard to believe? I personally have seen Gangnam Style more often than the zapruder shots or the moon landing. Heck, i've seen the clip "Aaliyah - are you that somebody" more often. This is not about the number of unique viewers but rather total views. Gangnam Style is easily the most viewed videoclip ever. Overall i think it can only be outclassed by long running commercials and tv show intro's.
It's absolutely impossible to believe. In the 1960s, the Apollo 11 moon landing had about 500 million views. The suggestion that in the four decades since it has not gained at least 300 million more is...well, impossible to believe. "An estimated 500 million people worldwide watched this event, the largest television audience for a live broadcast at that time."
It is that hard to believe. I've watched Gangnam Style twice, maybe three times, and I know lots of people who have never seen it at all. I've seen the moon landing footage dozens of times, and I don't know anyone over the age of 10 who hasn't seen it at least once.
You have to watch out for association bias. If you haven't seen the video very many times it is likely that your associates don't watch the video much either. But among other circles it has quite a bit more exposure than would seem reasonable.
