Here is how I understand that Sony prevents unauthorized programs from running on their Play Stations. Sony, together with Phillips, patented some of the essential techniques and formats for the CD. It is infeasible to build a CD writer without licensing these patents. Sony can impose a condition on these licensees that such hardware be unable to write the patterns that the Play Station requires. Thus Sony alone can build such writers and produce the CDs that the Play Station requires. This paragraph is surmise on my part.

A scheme such as this depends as well on tamper resistance, but tampering with the physical layer of a CD reader or writer is much more difficult than tampering with even the heart of a general purpose computer such as the PC. Tamper resistance may work here. Also there is no crypto key to be spread after hardware compromise. N.B. Patents expire.