If the controversy were over copyrights (presumably JD holds a copyright on their label), where the book cover reproduces that copyrighted work, then I'd get it

If the controversy were over copyrights (presumably JD holds a copyright on their label), where the book cover reproduces that copyrighted work, then I'd get it. The T-shirt would be subject to the same copyright concerns, and need to license the image. But the referenced letter explicitly says it's a trademark issue. I can't see how consumers are potentially confused between a book bearing a particular product on its cover, and that product itself.