Streaming music

This may sound like a stupid question but Im gonna ask it anyway. With all the streaming music services out now, I was trying to decide on which one I wanted to use. So to make sure it wouldnt count against my data package on my iPhone I called AT&T and asked is music streaming counted against my data plan and they said yes it did. I was wondering what is the value of streaming music if it is going to cost you in the end, I know it gives you a way to find out new music and playlists and such but if it counts against your data usage why not buy the songs you like on iTunes and play them and not chew up your data plan listening to music. For example, I asked the AT&T rep how long I could listen to a streaming radio service for and how long it would take to use up one gig for reference and he said about 8 hrs. This got me thinking how do people justify using streaming services if it uses up your data plan? I hope I worded this question where it is understandable and I know it sounds different but I just wanted to get peoples opinions on this subject. Thank you in advance.