Reality shows where people are pushed to their limits or documented for their bizarre qualities is a modern answer to the original yet forgotten arena for the weird and wonderful of our species: the circus.
More specifically, the freak show varieties. The strong man, the fat lady, the gypsy, the wacky, goofy, strange and plain scary. The fascination with the odds and ends of our society have indeed evolved however, to focus more on the mental strains upon people on competitive shows like The Biggest Loser, Survivor, The Amazing race, Masterchef.
As for Jersey Shore though, I still think it's all about the freaks.