How could that be against any law? If it makes no reference what so ever about playing Blu-ray discs, it's not a Blu-ray player. (Thus the giant 'Xbox' GAMING SYSTEM logo on the box.) If it just happens to play replicated blu-ray movies, then hey, cool bonus feature. But if they aren't flaunting that it plays Blu-ray movies _at all_, then there's nothing you can complain about when you discover that it can't play EVERY Blu-ray movie disc. (I've never seen one in person, so I don't know exactly what's on the box or system).
I'm sure if people complain enough, they'd be happy to remove the Blu-ray movie playback completely, that would solve all their complaint problems.
I'm sure their stance would be 'If you want a Blu-ray movie player, buy a Blu-ray movie player.'
And, if the official Blu-ray logo is _not_ on the box, manual or system, it is not required to adhere to _ANY_ blu-ray movie playback requirements (as it's not officially a blu-ray player).
(Just out of complete curiosity (and totally off topic), does it play normal audio CDs? I was really surprised to find out the PS4 doesn't do that...)