Well, horses don't actually need raincoats, any vet will tell you that... Left outside, they actually grow pretty protective coats. But I always remind my vet that horses do not natively live wild in this climate either, given a choice, they migrate south in winter.
I blanket Bay because if I do want to work him in winter, life is a lot better if he doesn't have three inches of hair.
The first year, I didn't blanket the pony. She doesn't do any work at all, and it wouldn't really matter if she grew three inches of hair, under most conditions she would be just fine. That is probably what is happening with the two you saw. One is probably going to be used this winter, the other isn't.
Then we had a bad storm. Six inches of snow, which then turned to freezing rain.
I didn't have my closed stalls in the barn yet, only their loafing shed which is under trees. The heavy ice and snow was cracking branches that were falling on the roof of the shelter, and their instincts told them to get away from the trees. So they stood out in the weather.
Bay was OK... His blanket keeps him perfectly dry, but the pony got soaked through and was in serious trouble. The rain fell on her and froze... and she was shivering with her head down. I think she was in real danger of becoming hypothermic.
I didn't own a blanket for her, I didn't have a place to lock them up inside, and I decided that would never happen again. I brought her in the lean-to and brought out every towel in the house and a spare comforter off my bed and started trying to get her dry and warm. I went to the store and bought her a blanket. A relatively cheap one, for emergencies. I still planned to only blanket her during really bad conditions, but Bay wears his 24/7 once the temperature stays below 45, so I gradually just started leaving hers on too because I felt the same as you when I looked out and one was protected and the other wasn't ;~D
And I built their closed stalls the next summer, so that I would not be stuck again with no way of getting them out of storms like that... Only put them in during extreme conditions.... Heh. Now they are put in most every night it might sprinkle. I am just a softy... But I am so grateful for the ability to not worry about them.
This year she got a premium blanket like Bay's new one... (This pic is last year's coats) I need to take a picture of them in their new blankets... they got really good ones this year, on sale, and they match ;~D
