Like NSE, I am not a fan of the frosted affect on the ramps. For a start, it makes the ramps feel really dark and gloomy, and it doesn't stop you knowing if a train is due to leave for a few reasons
1. There is a big departure board at the top of the ramps where live running information is displayed
2. If there is a large crowd of people coming up the ramp for e.g. platforms 5/6 in the evening peak, you can be pretty sure a southbound train has just arrived at one of those platforms
3. You can hear the diesel engines of any Uckfield trains when you're on the ramp, if one is in the platform
4. At the top of the ramp, you can see through the vent at the bottom of the windows and see if any trains are on the platform.
In order...
1. Yes, but each train's information disappears from the boards at a pre-set time before departure, so that trains are not advertised which are unsafe for people to try to reach before they leave.
2. Which means that trying to run through them will be challenging (albeit a popular sport...) and usually results in people missing their trains anyway. By the time the bulk of the crowds appear on the ramps, most people who were waiting on the platforms have boarded, and the train is preparing for departure.
3. For many passengers, diesel does not necessarily equal an Uckfield train. Some of the Uckfield regulars still don't know that their trains are diesel powered (yes, really! I talk to a lot of them...), and on the flip side, when the diesels arrive at East Croydon, the conductors and platform staff regularly get asked if the train goes to Purley, Caterham, Redhill, Brighton etc.
4. Not something a lot of people do, if I'm honest.
As mentioned upthread, the super-slick stairs seem much worse to me for safety than people running on ramps, especially as falling down a staircase is likely to be more likely to cause injury than falling over on a ramp. However nothing appears to be planned to rectify that.
I believe the stairs have seen considerably fewer incidents than your post suggests. The ramps are far more risky, which is why so many mitigation measures have been put in place there, and not the stairs. The station management of East Croydon would not have focussed all the attention on the ramps if they weren't the dangerous bit.
The apparently slippy surface and steep gradient of the stairs does mean that people take greater care when using them.
Would they? While it's not universal, it is obeyed more often than it is not on the Tube, at least to an adequate extent to allow flows to be managed reasonably well. And almost everyone who is arriving at East Croydon in the evening peak will have used the Tube.
The stairs at MKC have directional markings and they are *mostly* observed, again enough that people coming up aren't an obstruction to people going down to the point that they can't get on the platforms as was the case previously. One person on the wrong side isn't a massive issue, really, it's just ensuring one side is much quieter than the other so movement on both sides is possible.
I interchange at ECR a lot in peak, and I don't think a central railing is necessary. It's not as busy or as narrow as a lot of tube station corridors and it is generally not a problem walking against a peak flow.
Also, I don't think your assertion that 'almost everybody' arriving at East Croydon in the evening peak will have used the tube. There is a significant proportion of passengers who arrive/depart from London Victoria and London Bridge by foot or by bus. I vaguely recall reading in that at London Bridge, more people arrive by foot/bus than by tube, which I could certainly believe as the pavement on the bridge over the river is always very busy in peak.
Central railings are not always a good thing. You only have to look at the crush in the subway at Stratford each evening.
As for the Tube point,
maniacmartin is probably right. Not only do the London termini have large numbers of foot, bus and cycle passengers (not to mention the odd river bus passenger at London Bridge, and those using taxis etc.), but there's also the West London Line service and stopping services via Clapham Junction, trains via the Blackfriars area where many people board from street level without touching the Tube (City Thameslink doesn't even have a Tube station...).
Oh, and all the commuters from Horsham, Crawley, Gatwick, Redhill, Haywards Heath, Three Bridges and Brighton (certain trains in the evening around 1730-1800 are full and standing from Gatwick or Earlswood to London...).