Ken Dodd triple album:
The Guardian (amongst others) has been enjoying in-store pricing oddities for a while and, on the face of it, there's something not quite right about this Amazon item either.
But would you simply chuckle and shout bug?
Let's make it an exercise in creative thinking to suggest scenarios where it's reasonable for it to be cheaper to buy the CD and the MP3s than to buy the MP3s alone. Stick 'em in the comments if you like.