New Pricing Model for iTunes

According to this article at Forbes, Apple wants to charge more than 99 cents for popular songs and less than 99 cents for less popular songs. The question is who will decide the popularity of songs? May be they will start with 99 cents and if everyone is buying it then it become popular and Apple will increase the price. On the other hand if a song is doing badly in sales, they will drop the price. Any thoughts?