The point I think most are missing is that tyre size, tyre type and tyre pressures are all very important parameters to consider, but from what I can see most people who have trouble in the snow simply don't understand how to drive a car in slippery conditions, or even realise until it's far too late after it's broken traction, and then freeze in panic.
I spent all of last winter driving around in a pug 306 estate with all-season tyres, up and around mid scotland in a variety of conditions from hard-packed snow/ice to 8-9" deep fluffy coverings and never ONCE got stuck or slid off the road, and I put that down to practice and knowing the feel of the car. Whenever it snows I'll take it somewhere safe to re-learn the limits. Whenever I'm driving, if it's safe (wide bit of road, approaching an empty roundabout etc), I'll attempt to push the limits to figure out what the local conditions are in a place I can recover it easily. I try my tyres at different pressures. I CHECK my tyre pressures - 4psi makes a WORLD of difference in grip and contrary to how the big 4x4 guys do it, lower pressure doesnt seem to help my tyres at all, it builds up a central belt of snow that loses traction.
Mate has them on his Quattro p reg A4 (alps car) he was flying through the northumbrian snow at the weekend. Better than any 4x4s
That's quite interesting as I drove past 2 Quattro A4's yesterday, one stuck spinning in place in a petrol station and the other struggling up a B road spinning all over the show! I'd expected them to be notably better than they appear to be from my experience!