If a robin's feathers get plastered down with a layer of icy rain, it could easily succumb to hypothermia. Robins can easily shake off any snow falling on their feathers. Since robins won't be feeding on the ground anyway, a foot of snow there wouldn't affect them much, and not nearly that much snow would collect on berry and apple tree branches. Snow that collected on the branches would drop off when robins alighted on the branches, so they'd be able to find food. Food is THE most critical need a bird has in cold weather.
Food fuels the robin's metabolism, giving it the fat and energy to feed, move, and survive.
Last time we talked about robin behaviors reported by Journey North observers. No other songbird does this unusual behavior. Next, the feeding observations. In fall and winter they feed mostly on berries and other fruit on a wide variety of shrubs, trees, and vines. Over the next several months, create a list of robin behaviors you observe.