I didn't really find it funny either - it seemed like they set it up, knowing he can't make it over properly. "Jackass" type stunts are for people who can make their own choices - not animals.
My cats do stuff like that all the time, and it is rather amusing. What makes it funny is that cats are normally so graceful (so I've been told; mine are pretty spastic most of the time) that to see them be clumsy is unexpected.
I didnt find it funny.. but I do laugh when people fall, infact I laugh the hardest when I fall after the all you know pain thing and crying subside, but I thought it was just.. wierd the way that cat jumped... It just bugs me for some reason.. or it could just be late lol but yeah I think it might also be a set up... the cat didnt hesistate to jump it so it must have jumpd it before and cleared it, with my cat when it comes to jumping she'll look at it for a long time, try to find another way up over it sometimes or just jump it.... it.. bugs me