He most likely did have cross plys in those days. What he said though is not necessarily wrong today but it depends on the tyre. Cooper and Micky Thompson for example do say to reduce pressures in off road conditions and no doubt many other manufacturers say the same thing. I fitted these things
http://www.goodyearautocare.com.au/TyreDetailAction.do?website=GAC&websegmentcode=RV&mtpcode=00120&from=nPerPage in 205 size to my Lux seven years ago and, seeing the factory recommended pressures looked ridiculously low at 25 front at all times and 25 to 34 rear depending on load, I rang Goodyear's technical informtion number for advice.
I was told to use the factory pressures; do not reduce them off road; never exceed them by more than 4 psi; each 1 psi increase at the rear will support an additional 70 kgs and their testing has shown the 4psi rule is not accurate due to too many variables.
Since then they have been everywhere from the freeways around Sydney to the Victorian High Country to the Gunbarrel Hwy and many other Outback tracks on the same pressures I left home with. The wear has been even right across the thread and I have yet to get a puncture. That does not mean they are puncture proof, I just haven't run over anything capable of causing one yet. I must also add the car has always been well under GVM on all trips so it has yet to go anywhere with 34 in the rear.
I would always recommend ringing the manufacturer of your tyres whenever you buy a new set. Nobody knows more about them than the people who designed and manufactured them. Your car's suspension has been designed to work with the standard size and specification tyres and the recommended pressures are a vital part of the design.