I realize they aren't entirely comparable, but if someone just died from blunt force injuries from having his upper torso slammed around, they might be comparable enough. (I realize that's not a delicate way to say it, but I say it to highlight the seriousness of what happened, not to be disrespectful to the victim here.)
That said, we don't know what happened yet. If it turns out this was from something like a malfunction on the ride (lap bar coming up and hitting him in the head for example) then ok, maybe I can accept that a coaster is that much more controlled that the need for higher level restraints isn't there. For me it depends on whether or not this was due to his torso being unsecured. If it was in fact due to an unsecured upper body - I think that's a no brainer, lap belts don't cut it for a ride like this. But again, that might not be the case.