I don't think it's just PADI that teaches that a mask on forehead is a sign of distress, I'm pretty sure at least some of the other agencies teach it too. If you watch a distressed diver hit the surface, two things are going to happen almost every time... regulator out of the mouth and mask off the face, it's practically a race to see which happens first. It's gonna happen.
The trick is it's a "sign of distress", it's not necessarily a sign that a diver is distressed. I'm pretty sure the whole backwards thing was started by people who realize a distressed diver most likely WILL put their mask on their foreheads and that placing a mask backwards shows purpose, not panic. I think when someone barks at a person for having a mask on their forehead they're probably overreacting a bit, mentioning afterwards that some people don't like seeing masks on foreheads because it's the first thing a panicked diver will do doesn't seem like that bad of a thing though.
Personally, I keep my mask on my face 'til I'm either on the boat or on shore if shore diving. The majority of brand new divers I get on board try to hand up their masks first, then take on the battle (for some of them anyway) to remove their fins. If they'd just keep their masks on, they could see what they're doing. I've seen a number of masks washed off the swimsteps on choppy days over the years on boats I've worked off of, on night dives they've lost their masks, simple solution would be to keep it on 'til inside the boat in my mind. In general, it's my opinion that the larger portion of divers I see coming up the ladder with their masks on tend to be the more experienced divers.
