What does Unlimited mean for yahoo music? Why am I asked to purchase songs?

Answer 1

Yahoo Music Unlimited is a subscription service. If you subscribe to it, you can download an "unlimited" number of songs from their licensed library (which itself is not unlimited, obviously), and listen to them to your heart's content (while your subscription remains valid).

Yahoo Music also is a seller of songs. If you buy a song and download your purchase, you can listen to it "forever" and burn it to a CD, regardless of the status of your YMU subscription. In fact, a YMU subscription is not required to buy songs (although the price is lower if you are a subscriber).