I think the distinction is between software and hardware DRM. DirecTV controls the entire hardware chain. This means they can do various proper encryption schemes (public/pre-shared key etc) that are actually near impossible to crack and make it really, really hard to obtain the key by making the key write-only in the crypto-chip.
In a pure software solution, you control the hardware, and any hiding of the key is subject to reverse engineering the software.
In a pure software solution, you control the hardware, and any hiding of the key is subject to reverse engineering the software.