I take it you're in a warmer climate, a regular blanket is insufficient for many months of a year here. Like growing up, I had multiple blankets and a duvet, and had similar in some less well insulated houses I've lived in. My current house is better insulated, so a duvet on its own is generally sufficient.
I don't know what you consider to be a warmer climate, but I'm in the midwest US and it goes from around -10°F to 110°F here throughout the year. The temperature outside has pretty much nothing to do with my choice of bedding though, because it's always within 1° of 67°F inside my home unless my HVAC system is broken.
I know a lot of places aren't as into complete climate control as we are around here, so it makes sense that those places would have different priorities when making bedding choices, now that I think about it. Thanks for sharing.
Here in scotland, uk, in winter, the interior temp of my house will drop to 16 or 17°C overnight, from its regular temp of 20/21°C during the day when the heating is on.
Outside temperature range round here is maybe -6°C to 24°C
I don't know what standards the RoW uses, but we have a TOG rating here for our duvets ... we have a 4 for summer, and 13 for winter.
