ANY design of any structure will include compromises.
Not every measure for safety can be implemented for a million different reasons, starting with the inherent danger of an open train platform in the first place.
The issue here isn't really that the design of the platform is bad - it's probably served millions of commuters without much in the way of safety incidences such as this. The issue here is the pram/stroller.
A strong gust of wind won't do much to push a regular stroller - one of the rigs I push my sister's twins around in has worthless ball bearings. On the other hand, she also has one that more or less moves on its own because the action is so smooth. From looking at the size of the wheels, I'd say it looks like one of those exercise runner pram thingies, which tend to run towards the high end.
I don't blame the mother, as this kind of thing could have happened to anyone, but to push the blame on to the design of the platform, which is an almost universal design used all over the world is also the height of folly.
A platform where the water flows away from the edge is a much harder to build properly and will inherently have more pools of standing, shallow water. Perfect flow is more or less impractical. Add any number of surfactants, oil, etc. In a situation like this, you'd actually be creating much more in the way way of possible slip hazards on the platform itself.
Assuming that's why it slopes down. I don't really know, because I don't design train platforms.