WHY DOES THE IPHONE NEED TO BE ON A WIFI CONNECTION TO ACESS ITUNES MUSIC STORE?

I assimilate wifi and everything, but there is one thing I do not get. How come apple done the iphone song store which you have to be on wifi to entrance it? I know which corner entrance would be slower, but which can’t unequivocally be an excuse. Edge and wifi make use of the same internet, so because can’t both entrance the itunes store?