The post below (and the associated thread) gives the history and background behind the current official rule wording regarding traps:
Rokkrwolf wrote:I've spoke with Intelli about this quite a few times in the past. I will state it again here and also mark it in the official rules so people can find it easier.
"Traps" are allowed to be made. They cannot be built near spawn or off a main path unless marked.
"Traps" are allowed in the nether as long as they aren't within 50 blocks of the spawn portal. The same goes for the End except the spawn point instead of the portal. As for the Wilderness it's free game.
In this case Ori is correct, the traps is off 1 of the 4 main paths out of the realm which isn't allowed unless marked. So aksys will be banned, I will note he hasn't been on since the 25th, so it's not like he could fix it atm, I have went back and blocked off that traps so no one else dies by them.
In this particular case, OrigamiElephant was dropped inside a walled plot by the teleporter. There were four 1w x 2h tunnel exits from the plot, one in each wall. One of those was trapped via a hidden pressure plate (stone pressure plate on smoothstone) and resulted in Origami's death.
The ruling in that case was that the trap was illegal because it was laid without marking on one of the main paths into and out of the plot. As such someone travelling through the landscape and minding their own business could quite easily fall prey to it.
I haven't seen the trap that bendrake died in as he hasn't provided coordinates, but I note that it was set at the entrance to a building and required him to press a button. That feels less like "main path" to me and more like stickybeaking someone else's build. Not that there's anything wrong with stickybeaking (I do it myself quite often) but as soon as you stop travelling and start interacting with builds, I would say you're no longer on a main path and setting of traps is allowed.
Rokkr will correct me if I'm wrong though