As a 360 driver i can answer this one
It is because of the DOO equipment on the platform, when we operated 4 car 360's we had special signs made (at horrendous cost i might add!) attached to a lamppost. now all our 360's lengthened to 5cars we use the existing DOO equipment for the length of our train hence why we stop at the end of the platform at Hayes for the DOO cctv (which incidently doesn't work for ours!!! so manual lookback is used),
At Southall we use the CCTV screens at the end of the platform much to the delight of the locals who all try to jump into car 5 all 400 of them lol!!
Hanwell and West Ealing the screens work, although EB is a bit hit an miss sometimes!
Down services use DOO mirrors at all stns except hanwell
One of the reasons for FGW turbo's stopping at the last stop point (slough for instance) regardless of length of train, is due to an incident quite a few years ago when a 6 car unit (2 coupled) stopped in the middle of P2 and released doors only to find that car 6 and i think car 5 weren't on the platform and you guessed it some pillock opened the door and down they went!
In the good old days one always checked to see if you were on the platform before opening such door and leave the train, nowadays we have to assume that all pax are thick ****s willing to sue at first instance so we get procedures like this
