I am curious. Do you have pictures of the service transformer? Or where the primaries fell?
And if there was any lightning the night of the storm?
The easiest explanation, would be that the primary crossed on one phase, at the transformer terminations. Bring the High voltage in along the main service conductors. And jumped in the panel, on the circuits that were more "open" down stream leaving no path ground. Then the damaged branch circuits, that were under load *ie have less resistance to ground* during the increase in voltage also took the hit.
A unlikely explanation, would be that the primaries fell somewhere near the grounding electrodes, raising the reference voltage. Sort of like Stray voltage concept that Mike is always talking about.
I completely just made all of this up. But does it sound like it makes sense?
