utility's responsibility to properly address their balancing authority. They have SO many tools in their tool box to do that that are infinitely more effective then depending on your or me to bump the thermostat up a few degrees.
I work for a 8,000 megawatt peak utility in Arizona. Historical data tells us that at BEST we can expect a 100 MW decrease from consumers through pricing incentivization ("please use less energy" type programs). That's 1.25% of our load. It's a tool, we'll use it, but there is still the other 98.75% of demand we have to address and remain responsible for meeting 100% of demand 100% of the time.
Utilities have planning departments, real time, day ahead, and long term energy traders, they have their own resources, all to address supply and demand.