I assume they no longer believe everything else they were told in the 1970s or 1980s [...] but somehow their views on 'race' and ethnicity remain preserved in aspic.
This! Reading some of the posts here, you'd think the terminology had changed every year for forty years, with each new word sent out in top-secret to a limited mailing list of people who would JUDGE YOU for inadvertantly slipping up.
Is it just a race thing, not noticing which words have dropped out of widely-accepted useage? Did you get the memo about 'spastic' (hey, we had a Spastics Society until 1994) and 'cripple' and 'the retarded boy'?
I come from a rural, non-diverse area where older people often still say 'coloured'. There is usually an awkward little pause before the word, sometimes out of sudden uncertainty ('oh shit... that doesn't sound right; when was the last time I heard or read the word 'coloured'?; but I've started so I have to finish'), sometimes from a sense of delicacy ( 'I mean BLACK, of course, but I should hate to be so crass as to refer to that disadvantage'), and occasionally with visible distaste ('this... [ugh, can hardly say it]... coloured chappy').
IME, the first set of people are embarrassed but responsive if you say anything, the second are a bit grumpy ('what? I'm trying to be polite! I can't just say BLACK, that's terribly insulting'), and the third will go off on a PC-gorn-mad rant that generally throws in as many offensive terms as possible.
And there's always the 'no offense intended, so nobody is allowed to feel offended' response. I appreciate there might not be overt racism in using any term, but a complete lack of interest in or respect for how groups of people choose to define themselves is, in its own way, offensive. Yeahyeahyeah, black, coloured, whatever -- can't keep up, can't be bothered.