You'd want a combination of storing the keys in tamper-resistant/tamper-responding FIPS 140-2 smartcard module (like a TPM), and some kind of certificated key architecture (where each mac and each airport have a key signed by Apple, but where breaking a single device and extracting the key isn't a class break -- it only provides the ability for everyone to stream to or from that one physical device. That way the Apple Signing Public Key can be in everything, but the Apple Private Key can be kept offline in Cupertino. You could even do a multi-level system where there are manufacturing keys signed by Apple's key so the contract manufacturers don't steal things.

Combine that with a way to update and blacklist keys and devices, and you have the state of the art DRM type system. The cryptography used in the BluRay format is probably about the best currently deployed in that application, and can just be bypassed. The same people (Paul Kocher's Cryptography Research; IMO the top cryptography consultancy in the world) who developed that developed the original Divx system (video rental at Circuit City) did the crypto for BD+. http://en.wikipedia.org/wiki/DIVX

TPMs are unfortunately usually only FIPS 140-2 level 2 or 3, and not THAT hard to break a single instance of. The TCG's TPM architecture is such that compromising one TPM doesn't class break everything. If you naively put a global key into a low-security module like that, and put millions of them in enemy hands, you will get screwed by someone with some acids and an electron microscope at college (or a competitor leaking it anonymously)

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.