When I was a child we had sheets and blankets on our beds. The top cover was either a rug or an eiderdown which was easily discarded in hot weather. What is an eiderdown? It's a quilt originally filled with down from of the eider duck and used on top of the blankets.
In 1964, just 6 years before I married, Conran introduced duvets (otherwise known as 'downies' or 'continental quilts' in the UK , 'comforters' in the US and 'doonas' in Australia). We bought our first duvet in Edinburgh before we married. I have never slept under anything other than a duvet since.
The only slight disadvantage to duvets over blankets is that one has to keep a variety of different warmths (ie tog ratings) for different weather. I'm fortunate to live in a well-insulated and generally warm house but I like a cool bedroom. I use a 13.5 tog duvet in the winter and a 4.5 in the warmest weather (ie at the moment).
Okay, so this is looking like a really boring post. Indeed it is a really boring post. The excitement comes when guests are arriving. Which duvet should I put on their bed? I can choose from togs 4.5, 7.5, 10 or 13.5. Now there's a First World decision for me.