There are two basic factors regarding traction in the snow, all wheels/tires turning (not just one spinning while all the others don't) and the road surface. Subaru is the only AWD type vehicle that has true positraction on all four wheels, other than larger 4WD vehicles like Jeep and Isuzu Trooper (there are others). But, if you are on ice, it doesn't matter how many wheels are turning if the road surface is slick; you will not get traction, especially going up hill, UNLESS your tires can "dig in" to actually grab the road surface. Snow tires have little spikes or nubs that will break the surface of ice. Chains do the same thing, hence the benefit chains provide when you don't have snow tires.
It is true that most SKILLED Subaru drivers can go most everywhere without ever having to use chains, there are always those special circumstances then you can't move in the direct you want due to the specific conditions of the road surface.
I carry chains in my Trooper and have used them, and they helped. The same is true for the Subaru (I just have to find the right ones to fit).
My wife drove our 2013 OB in the snow for the first time yesterday. There was about 6 inches of snow on the driveway when she got home in Grass Valley, CA. It did not slip sideways once where here 2000 Volvo AWD would when making the turn from the street into the very long driveway. And when she turned the the Subaru around to back into the garage, it did not slip and slide like the Volvo used to do, so she is a happy camper.
