I certainly experienced what can happen when you have a surge without a ground. One of the receptacles in my apartment had a broken ground. Just before my new wife and I were supposed to go on our honeymoon, I found the surge protector smoldering. The MOV blocked a surge, but since there was no ground to divert the power to it had started handling the current itself. If we had not been home, it may have caused a fire. I have a pic I could find and post. That being said, better surge protectors with multiple MOVs can handle these situations safely, but since this technical detail is often lacking I'd rather have a ground available.