Are there any reason based on physics behind having commuters stand behind the yellow line on the platform?

I would have thought the obvious one, here in Japan anyway, is that at rush hour the platforms are dangerously crowded with people lined up, and others walking all over the place, it would be very easy to get bumped from behind, and it happens all the time, so the further away from the edge you are, the less likely you are to be pushed under a train as it comes in.

I don't like to stand near the edge when it's crowded. There are drunks staggering around, people reading as they walk and just plain rude types who couldn't care less if they knock you as they walk past. It's best to leave yourself adequate margin for error.

There are at least two reasons " based on physics" that I can think of.
The first is based on Bernoulli's Principle which, briefly stated, is that as the speed of a fluid increases, the pressure within the fluid decreases. Maybe you remember it from simplified "How an Airplane Flys" explanations. In this case the fluid is the air and it is the train moving through the air rather than the air moving over a surface but the principle is the same. If the train is moving fast enough it creates a layer of low pressure all along its length, if the pressure is low enough and you are standing close enough, you could get sucked right into the train. The pressure is even lower under the train and you wind up getting sucked under the wheels.
The second reason is based on Newton's Three Laws of Motion;
1. Inertia. Every object remains in a state of rest or of uniform motion in a straight line unless acted upon by an outside force. ( An object at rest stays at rest unless acted upon by a force, an object in motion stays in motion unless acted on by a force.)
2. Acceleration. The acceleration of an object is directly proportional to the net force acting upon it. The constant of proportionality is the mass. ( How fast something moves depends on how hard you push it, lighter things move faster than heavy things from the same amount of push.)
3. Reaction. For every force there is an opposite and equal force. ( Hence the Sith)
The first law comes into play when you are standing on the platform and another commuter comes rushing up and bumps into you. The rushing commuter's inertia is transferred to you and you stumble and fall off the platform in front of the train.[ The actual falling brings Newton's theory of gravity into the situation. Fg=G(m'm"/r squared), where Fg is the force of gravity or; things fall down, go boom.(Of course we must remember this, like evolution, is just a theory and not a fact and things probably don't fall at all.)]
The second law applies if the rushing commuter is a big fat guy and you are just a wisp of a thing, his proportionally greater mass is gonna accelerate you right off the platform. Where the even greater mass of the train will really accelerate you. (The effects of the first two laws demonstrate an even older law of physics, this time from Aristotle. Two masses can not occupy the same space at the same time.)
The third law actually means that you push against the train as hard as it pushes against you, but the train's greater mass and inertia means it wins and throws you way down the track.
The inertia (1st law) of the train makes it impossible for it to stop before it runs over you. The train and its wheels are going to mash, smash, slice, dice, and even julienne you, and it's just that easy, demonstrating Ron Popeil's Principle.
The Ronco Corollary, it cleans up in just seconds, does not apply.