Interesting. So why didn't they use a TMP? Cost savings? International distribution constraints? (I see TPMs are illegal in China -http://en.wikipedia.org/wiki/Trusted_Platform_Module.) It is somewhat peculiar given Apple's known DRM policies.
Probably cost and lack of effort. Just look at the iTunes / App Store DRM. It can be removed quite easily, it's mostly there for deterrence. As soon as Apple could, they dropped DRM on iTunes audio files by switching to iTunes Plus (and before that, you could burn the songs to a CD and import it back).
You'll find a quite different story when Palm made the Pre compatible with iTunes through reverse engineering. The certainly didn't want non-Apple devices in the iTunes ecosystem and spent quite some effort to put a stop to that, even though it had nothing to do with DRM.
