I'm not an EE so I can only guess. I've had experience with things like cheap candelabra bulbs blowing out and frying the X10 device they're on (twice). And I know those dead X10 devices worked fine the night before the computer on my stove blew out. Two more datapoints: there was a sconce light in the kitchen extension that randomly turned on about a week before the stove's computer went dead and the living room X10 transmitter could no longer reach one of the X10 receivers. The computer was replaced yesterday and these problems didn't happen last night.

My tyro guess is that that computer was generating some serious noise on the powerline before it eventually failed completely. When it did fail, it might have sent a spike that fried those devices. I'm ordering an X10 powerline filter for the stove just in case, and one more for the microwave (which is also Frigidaire).

I have no idea if Insteon devices are any less vulnerable than garden variety X10. Maybe it's just wishful thinking but the Insteon devices seem to be more substantially constructed overall. I'm hoping that carries through to their circuitry.