Of course, you don't need a Nest to learn to change your habits. Just stop using the HVAC, and you'll come up with alternatives. In my case, a mixture of fan usage and blinds/window usage.
It's easy to say you could achieve the same thing without it, but facts show most people don't.
Yet I suspect that very few of the people who bought the Nest actually care about energy usage, or reducing it. It is a lifestyle product and is a talking point, and while there are some who really desire it for that, many more set it to a static temperature and forget it. I hugely doubt that the total set of Nest users have seen any measurable decline in usage.