[mtdjed]

I am not an expert on the subject but rather a multiple victim of power surges. For the most part Lightning arrestors are not for surge protection but rather for a direct lightning strike on the protected structure. Lightning bolts are not random shots from the clouds but rather positive and negative charges attracting each other. So the idea of arrestors is to be the target should those charges be at your site and direct the charge to ground. However, if the lightning hits ground and finds a conductor such as a power line, cable, telephone line etc, it can then create a power surge. The surge may not be from your power line but rather through the phone or the cable line and I am told perhaps through water lines.
Power surges were less damaging in the days when devices were powered by motors rated in volts rather than millivolts.