Earlier quoted context omitted.
That's assuming you only ever run old Blu-Rays on that player. Blu-Ray has a thing called BD+ on it, which lets content companies run arbitrary native code on your player (among other things). It also lets you update your player's key revocation list for HDCP. So either of these mechanisms could be used to render your old purchased content unplayable.
Do you have any sources for this?
DRM stands for Digital Rights Management, but I call it Digital Restrictions Management cause that's what it is from users point of view.