It really is that, most Jackass pranks the joke is the jackass people themselves, with other people's reactions being part of the humour but usually not at their expense. The central source of the humour is the jackass people acting silly or humiliating themselves somehow.

CKY had a few bad ones though (throwing a life-sized doll off a motorway in front of cars is a good example of a bad one...) but they seemed to grow out of it.