I was under the impression that every blu ray inserted needs to show a certain encryption key in order to work. At some point if you dont get a firmware update on your player, it will stop playing newer blu rays. (In theory, its entirely within a blu ray players power to simply create a new player with certain keys revoked, meaning some or all of your blu rays wont play. But its highly doubtful this will ever happen)

I don't believe DVDs have to worry about any of this. Im probably wrong however. It's been a long time since I thought about any of this.