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.
