I’m not sure that all high chill apples do just fine in low chill areas. We’ve had threads about it, here’s one:
High Chill Apple in a Low Chill Climate?
On years when we’ve had very little chill, my Gravenstein has done poorly–as in intermittent blossoms throughout the summer and fall, and apples of all stages and sizes, many of which are still undeveloped in winter. And the “blind wood” talked about in the thread.
I think that many of the chill hour ratings for apple trees may be wrong, for the reasons Richard mentions above, which I hadn’t heard before–very interesting, and explains a lot! But this doesn’t mean that chill hours are not important for some cultivars.