Both Seth and Faris point out the subtle nuances that make this dance party take off.
For me, the big issue is authenticity. Would all those people have jumped up and joined in with a bunch of professional dancers? Probably not. As much as I love this Improv Everywhere-inspired bit from A&E, they are a self-contained group for the most part. Take a look at this recent MC Hammer-TV show promo event:
Fun stuff, but notice that no ‘civilians’ are participating. Some are bemused, some seem even a bit frightened at first. Compare that to the first dance video whic has a far more powerful vibe. You can feel the electricity and it isn’t manufactured, it’s real. As I noted in my earlier post, experience is important and you can see the difference in these two videos.