Actually it would be fairly simple to have a under/over voltage relay wired to a shunt trip main to disconnect the power. SOme of the new relays have a over/under frequency as well. These products are available today. I suspect the nuisance of having the house without power until it was reset, would outweigh the savings to the equipment. For the number of customers served and the few problems people have, I don't think it would be worth it.
Typically, low voltage harms motors, high voltage harms electronics. Over frequency can cause more problems than the over/undervoltage. Surge protectors and UPS can't protect from it.