No, it has always been the case that they show up on difficulty 5 and up (or it has been since 2.0, at any rate -- for a very, very long time). They show up less frequently on the lower difficulties, though. And, in 2.0 and perhaps a bit before, there was a bug that was quite often preventing them from showing up at all for anyone, especially in multiplayer. So that was probably what is making for the difference here.