Their marketing copy puts it into a murky area, too. "You have control over your music, so you can create tracks that do exactly what you want." That certainly implies you're the creator, in the same way that an artist who uses tools in Photoshop to make a picture owns the copyright on the picture, rather than Adobe (or perhaps more pertinently, someone who uses Garageband loops to construct a song owns the copyright on the song, not Apple). So I agree - the 'pay this much and it assigns you the copyright' seems like a bit of a dubious claim...