cathf, I think it's somewhat naive of you to assume that babies were almost all sleeping well in 1992. I can assure you that many weren't in the 80s, when I was born. I learned from many many many family and friends who provided sympathy and shared their own experiences when my own baby didn't sleep either.
I appreciate you mean well and are genuinely trying to share advice you think will help. Honestly, though, telling parents struggling with sleep that it's basically their own fault for not doing what you did is not as helpful as you might think. Especially since much of what you did is basic common-sense sleep advice that new parents are still being given now.
You say you can't imagine anything worse than broken sleep for 3/4 years. I'm dealing with just that myself, and let me tell you - it is indeed hell, but what's worse is going through that hell and having people pipe up with "oooh you should just do bath/book/bottle/bed and then not rush in at every little squeak!", like basic bedtime cliches had never occurred to me.
Some babies don't sleep, and many many babies aren't sleeping through the night at a few months old. That was true in the 90s, it was true in the 80s, and I've read a lot of parenting advice from the 1800s and 1700s and it was true then. There is plenty of scientific research into this - someone already linked you to the ISIS site, which looks at infant sleep research spanning different countries and cultures.
There probably are things the OP could do to try to encourage less waking (although I bet you she's tried many of them already), and of course those are worth suggesting. But soapboxing about how you have got sleep all cracked and the problem is mothers today bringing poor sleep upon themselves is not kind, and it's not helpful, and it's not even accurate.
(ps - no, this is not 'flaming' you.)