They're quite a bit older than this, assuming you're thinking of the British examples. The last Mark 3 coach was made in 1988, and the Mark 4s have sliding plug power doors.
It was still an odd design decision, though. There had been electric doors on BR multiple units since the 70s.
Yes it looks like I was thinking of those trains, they don't look this old. They run on the Reading-Paddington line.
Anyway, there's no excuse whatsoever for this design, however old they are!
After 3 years, I am still not quite confident opening those doors. I try to let another passenger do it for me.
Yes; derivative Mark 3A/B loco hauled stock was later also built for the West Coast Main Line (plus a bunch of sleepers).
I don't know whether the crash standards for 125mph running were higher at the time. The Mark 3s are generally very strong, and have held up to high-speed crashes better than their predecessors, so something was definitely done right.
They weren't fitted with central door locking until the early 90s, though, and even now it's not interlocked with either the train power or an 'actually closed' sensor - so it relies on the guard to make sure the train doesn't set off with a door open.
It was still an odd design decision, though. There had been electric doors on BR multiple units since the 70s.