Whether I shave off my higher-tiered consumption by changing my thermostat, changing my lighting or by putting in solar, that lost high-profit consumption isn't the company's property, it's mine to do something else with.
Their bigger concern is net metering, by which I can sell them solar power during peak hours at their retail rate of, say, $0.45/kWh and then buy it back from them at, say, $0.06/kWh at night, or maybe even 6 months later in the dead of winter.
Not paying for power you didn't use is one thing, but using the power company's own transmission network to arbitrage its rates with no fee does seem long-term unsustainable. If the current rates reached their ultimate conclusion, the power companies would have to make massive, massive investments in storage systems capable of buffering months worth of demand, as their net revenues trend towards $0.