The cost of putting in an extra underground tank isn't worth it if you must charge the same price ... hmmmm, you might be on to something here. Maybe a compromise -- companies can charge up to 20% more during a storm. It gives an incentive to solve the problem, and holds back the worst of criminal type behavior (lots of generators stolen from people's homes during storms - black market prices for them are high...supplies low)
The really funny thing is that when gas prices go up people buy more. They horde. Buy low, sell high.