That original copy has to come from somewhere. Someone bought the CD, converted it to MP3 and then put it up to be shared. That means, just like a used CD, the music has been purchased.
If you've ever done file-sharing, you'll notice that with one song you'll find many many different files. All the same song, but the bit rates of the mp3 compression may be slightly different, or the song length is slightly different, or the name is typed differently. This means that they are most likely NOT from the same source. Which means many people bought the CD, compressed the track, and then uploaded. So the record company is still making money.