American here, from the South. I've noticed the same sort of phenomenon travelling to the Canadian plains in winter, or among Northern transplants to the South in midsummer. Canadian sitting rooms felt like greenhouses to me (80+ Fahrenheit) despite it being 20 below outside, and my boss has commented before on visiting Southern households where the A/C is set to 68 in July.

My theory is that it's more about not-to-exceed ceilings [or the converse, floor] temperatures rather than average temperatures. When you have the huge temperature differential between the conditioned space and the outside, opening a door or something can affect the conditioned space's mean temperature by a huge amount for a short time. By over-conditioning or over-heating a space, you're more likely to be able to ensure the interior temperature never rises over ~75F, than if you'd set it at a comfortable 72F or so. Or in winter, it won't drop below a minimum comfortable temperature indoors when someone has to go outdoors.

Of course, once you've adapted to that habit, you may not always make seasonable adjustments to those settings.