Riding in snow (carefully) can be a lot of fun. I used to carry a hoofpick with me, as occasionally snow can ball up in the hoof, making the horse uncomfortable and possibly causing difficulty in moving. As for preparations, horses can deal quite well with snow, blanket or no blanket. I’d be more concerned about wet and cold, should it start out as sleet. So, with a horse who is out a lot, a blanket can be a good thing, so long as the horse doesn’t sweat under it.
It is never the horse's fault