You can save just as much money with a 1970s thermostat. You can save just as much money with a 1970s thermostat. Turn it down or off or up when you need to, simple as that.
Actually you can't. Physical impossibility. The 1970s thermostat for example can't modulate the boiler which would result in more gas being used to maintain the same comfort level in the room. That's before you realise that human behaviours prevent you from doing what you want to do. "Oh I'm only going out for 2 hours, I'll leave the heat on because I don't want a cold room when I get home". A smart thermostat can handle that for you without any loss of comfort, you won't, because you are a creature of comfort and can't reach your thermostat when you're 30min out from arriving home.
Ultimately you can say what you want, or pretend people do something that happens only in your head, the reality is that smart thermostats have and do save people money. That's just the fact. Anything you *could* do is irrelevant in the fact of that evidence.