In 40F water for 4-6 hours and you're looking at a severe case of death.

and even a mild case of death can kill you...be careful out there!

40F outdoors with clothes.

Ice baths are several minutes.

The faster the thermotransfer, the shorter the cold shock period, obviously...

I figured that was air, like "cryo". Later:

similar effects for immersion in cold water for several minutes as well

No kidding. Must mean 4-6 minutes.

IIRC the scenario was with clothing on where people spend extended period of time outdoors in the cold. E.g. shoveling snow, hiking on a cold day, etc.

Activity makes a big difference. Sitting outdoors for 4-6 hours without a coat in 40F would mean hypothermia for most people. Heck, I lose peripheral circulation and get sick more easily after sitting outdoors for just an hour or two in 50F WITH a coat if it's not an adequate one.

I am not sure how much clothes would help in preventing hypothermia.

Generally, quite a lot, as long as you stay dry. I spent 8 straight hours outside shooting pictures while standing - and occasionally lying down - on a frozen lake in northern Canada in January. It was -25C / -13F. I was perfectly comfortable, although I did have to repeatedly switch batteries with ones that I'd been keeping inside my coat.

Goal was to get pictures like this: https://goo.gl/images/imXCMy

(Those are methane bubbles frozen in the ice.)

"It's not the [lack of] heat, it's the humidity" applies in the cold, too :)

It's occasionally getting to -20-25 C during winters where I live, but people go around in their daily routines (only exception is children that do not have to go to school if it's below -20 C). I'm pretty sure if not the clothes, there would be a hell lots of frozen bodies around every winter.

Clothes are the reason people don't regularly die when they go skiing, or for that matter, live outside the tropics.