With Hymn, I suspect Apple only had two options: (1) go after them, or (2) get out of the music distribution business. At the time, the people who owned the music Apple distributed required Apple to use DRM. I'd be shocked if the license they gave Apple did not include a requirement that Apple do everything it could reasonably do technically and legally to try to keep the DRM effective.

As for Psystar, what about them? Apple has not gone after the hackers who figure out how to run OS X on non-Mac hardware. They've not gone after the numerous web sites that tell you how to do it. They've not gone after the book you can readily buy at B&N or Amazon on building a hackintosh. They've mostly looked the other way (hell, they have even been known to include in OS X updates bug fixes for problems that only manifested themselves on non-Apple hardware). It sure doesn't look like Apple has much of a problem with people hacking.