Now in my 51st year of licensed driving (scary thought) - so I've driven cars from the era of un-powered steering onwards.

I believe most of the posts on speed-sensitive steering have it round the wrong way... it's boosted at low speeds, because that's when you need it for parking / sharp turns. At higher speeds, as someone pointed out, steering effort naturally lightens up and powerful assistance would be just too much of a good thing.

So not so much reduced at high speed, as boosted at low.

Same result, of course.