As already adequately stated, the observed horses appear to be well maintained. As an aside, here in the western U.S. we have several working cow ponies that are kept outside. To help alay your concerns, a little additional knowledge about the horses natural winter coat could be helpful.
The lessening of daylight promotes a unique growth of winter hair. Not only is the length (guard hairs) noticeable, but more importantly the thickness (which may not be as readily observable) is greatly increased. It also contains a natural oil that sheds rain, snow and ice. You would notice this oiliness when currying the critter in the spring.
One might notice, in wet weather, the horse repeatedly shaking themselves. This too, is a natural function to not only remove some of the accumulated precipitation but to "fluff" the hair back up to provide insulation.
Lastly, the owners should regularly inspect the horses hooves. In wet, snowy conditions,the horse can accumulate layer upon layer of packed snow within the bottom of the hoof. This usually results, due to walking motion, a pointed "ball" of ice and snow that needs to be removed with a farrier's hoof tool.
The horses should have put on a little fat as true winter weather approached... maybe as much as an inch in the small of the back and over the ribs. Enough feed, in the way of grain, should be fed to maintain this fat layer...