Can't help but to unload my two cents....
In NE Nevada where it gets -20 in the winter, I never blanketed. Those horses were just fine with bifg fluffly coats. Even it it snowed and they had two inches built up on their backs, which meant they were insulated and not losing heat. They knew how to deal with the conditions. They knew how to break the ice in the river and dig through the snow to find the grass. If the snow got a big hard crust they got fed hay just like the cows.
Take them same horses and move them to NE Texas. Different ball game. Even though the winters may not be -20 and snowing. The rain and wind is what kills them, they are miserable! They are turned out in cow pasture with no run in shed(just like at home in NV), when the grass is no good I always have a round bale out in the feeder so they can munch on it at their leisure. But when it rains sideways and they get wet and cold and get to shivering I will admit to drying them off with a towel and blanketing until the rain stops.
The key to blanketing is the weight of the blanket, in my opinion. I understand the thought about a blanket laying the hair down and allowing it to fluff and trap the heat but if you blanket with the appropriate weight even if the hair is laid down from the blanket the insulation should keep the horse warm. For example, throwing a waterproof sheet on when it is raining, windy and 33 degrees....he most likely is still going to be cold, miserable and worse off than if he didn't have the sheet at all.
I DON'T LEAD 'EM AND FEED 'EM, I RIDE 'EM AND SLIDE 'EM.