The song is catchy and the dance means there's an incentive to have heard and recognise the song. Same deal as the Macarena (http://en.wikipedia.org/wiki/Macare

The song is catchy and the dance means there's an incentive to have heard and recognise the song. Same deal as the Macarena (http://en.wikipedia.org/wiki/Macarena_(song) http://en.wikipedia.org/wiki/Macarena_(song)) and Crank That (http://en.wikipedia.org/wiki/Crank_That_(Soulja_Boy) http://en.wikipedia.org/wiki/Crank_That_(Soulja_Boy)). The combination of the internet growing and gaining mainstream adoption (it's now "cool" to know about internet memes) and the "old medias" desire to be in on "new media" made it inevitable. Gangnam Style is just the "perfect" combination of everything needed to be a success. Also he attended almost every big TV show around, so after appearing on one or two big shows every show had to have him.