Don't think for a second that Sony was never going to implement DRM.
This is the Patent File from January, 2013.
They probably agreed to do it along side MS but decided to pull the rug out and make MS look like the bad guy.
A lot to read but here are some of the key parts:
 A technology of digital rights management (DRM) is introduced to prevent the electronic content from being used unlimitedly.
 Typically, DRM is a technology for the prevention of the unlimited copy of electronic content. To this end, the inventor recognized that there are cases where it is difficult to suitably restrict the use of electronic content, stored in the recording medium like DVD and commercially traded, according to the attributes of use entities of the electronic content.
 The present invention has been made in view of the aforementioned problems, and the main purpose thereof is to provide a technology for restricting the use of electronic content store in a recording medium according to the use entities of the electronic content.