Which, ironically, is exactly what Apple is protecting here. DRM.

DRM for your own data is called privacy.

Apple, a 3rd-party, holds the master keys, and you don't.

So no, that's not DRM for your own data.

But that's simply not entirely true. The encryption keys for the phone's data reside on the phone and are only available with the PIN/password.

Apple does hold the keys for software updates, which can be pushed without user approval. Maybe that's what you were referring to.