Thanks for the informed comment
A quick thank you to the informed sources who have commented to date (and those to come.) As a confirmed PPRuNe lurker with long experience in various facets of aviation ops, it was a shock to me to realise that I'd never had to get into the fine detail of what determines the need for de-icing on the ground, nor how it gets done in today's world.
So the steers to relevant sources have been invaluable. I've also been reminded that safe operations in icing or snowy conditions are very expensive in time, direct cost and indirect cost (people time, reduced throughput etc.)
This brought back a memory of being SLF on a jet where the first de-icing was not successful. There were well-meant if ignorant suggestions from some (management) quarters, keen to see the aircraft depart, that 'most' areas met standard and this was good enough.
This provoked some very very blunt responses for which I am now even more grateful. Classic situation where ground engineering and/or PIC can come under an awful lot of pressure to cut corners.