Legitimate reason for the watermark (Score 1)

Privacy issues aside, when you plug an ipod into another computer itunes prompts if you would like to transfer authorized itunes music store purchases from the ipod onto the computer. With the DRM-free music, there would be no way to differentiate between purchased music and ripped music. My roommate and I were wondering the other day how apple would make this distinction, and aside from not allowing transfering the DRM-free tracks, this is the only solution. I'm sure statistics will be collected all the same, but I do think the information has a legitimate, non-malicous reason for being stuck in the files.