Modern CPUs have transistors that are orders of magnitude smaller than the ones in your Amiga, and there is a direct correlation between transistor size and how much abuse they can take. Additionally, it only happens when the device is on (and for modern CPUs, not so much when idle, much more when the device is turbo-ing and actually at the high voltages). You can expect silicon degradation to become a thing you actually need to worry about as CPU feature sizes continue to shrink. It will probably never get to the point where they degrade faster than they become obsolete, though. (a dramatic reduction in cpu improvement cadence might do it)