So what your saying is if you had bought a cheap Lux thermostat that has a 2 degree swing. And programmed it for set backs. You would be saving just as much, still be less comfortable. But have more money in the bank.I have noticed the Nest sacrifices comfort for efficiency as the temp swing is about two degrees for cooling which is a little high (and cannot be adjusted). It was uncomfortable at first but I've gotten used to it.
PS: Your area had less cooling degree days in August 2012 then it did in August 2011. Only 4% less, but that is part of your savings.