True, but in many places there are benefits too. The MTR in Hong Kong is currently going through the process of having glass walls on all the underground platforms. The financial justification for this is based on only having to air-condition the stations and not the tunnels as well. The reduction in "jumpers" is just a fortunate side-effect.

The trains aren't fully automatic either - the drivers are just very good at hitting the stop point (and the platform doors are wide enough that they have an acceptable margin of error of ±18 inches or so anyway). Very occasionally they have to do an extra little "nudge" forward or backwards after stopping.