The one thing that confused me most: why was everyone laughing like it was a comedy sketch?!? I mean, yeah, the guy was funny, and he did a really good and humourous job of pointing out how absurd the piracy figures are by ridiculing the breakdown of them, but it wasn't that funny.
On topic, the reason they get those numbers is because they are estimating not just how much damage has been done to the existing media empire before the internet, but at how much the potential growth of the media industries have been stunted by piracy, and that allows them to generally make up whatever figures they like, because it becomes a purely hypothetical exercise, where accuracy is at the discretion of the user, and these guys are there to make piracy look as bad as possible.
It's a bunch of crap, but the horrible thing about it is that these clearly insane, inflated figures are being used to inform current and future government policy, laws, and most worryingly of all, court cases against people who have been caught pirating music, who being fined stupid amounts of money they will never have a hope of paying back.