There's a big difference between the earthquake case, where it's really unlikely that there's a dude who will actually set off a bomb, and here, where it's guaranteed that over the whole internet, there's at least one dude who is going to DDoS you. The fact that someone in particular actually sets it off and is therefore morally responsible for disconnecting all those users doesn't remove any blame from Ubisoft, who was releasing into the real world where the DDoS was guaranteed.