4 wheel drive does not help you on ice, all 4 wheels spin and you are super fucked. In most winter conditions, you are far better off with 2 wheel drive, the right tires and an abundance of caution.
...ummm. No. On any slippery surface, allwheel drive and 4wd will always drive better than any 2 wheel drive when driven with the same tires and care and attention.
And most 2wd vehicles are actually 1 wheel drive. The differential will always send power to the wheel that turns the easiest. Even a limited slip differential may not help, as the clutches need a bit of force to activate. At least with 4wd, you get 2 axle drive, so at least one front and one rear wheel will both turn. Odds are at least one of those has enough traction to get you moving.
If you have locking differentials, then you become like a bulldozer, all wheels must turn, and then you do get moving, unless you gun the engine and dig 4 nice holes in the deep snow.
If you have AWD, your anti-lock braking system is used to detect which wheel is spinning, and then selectively brake that wheel, and force the others to turn. Not a bad system, but the sudden braking and release of the individual wheels can cause instability, so don't go too fast, or you'll find yourself going down the road sideways.
With careful driving and good tires, I can get a front-wheel drive further into the slippery stuff than I can a rear wheel drive.
But with locked differentials on a 4x4, I can go pretty much until I'm high centered. If I need to, I can also let air out of the tires down to about 8 psi (still safe on my 4x4's over-sized tires), and drive on top of the packed snow.
Bottom line: all vehicles 2wd, 4x4, AWD, may change the number of powered wheels, but most vehicles are 2 wheel steering, and 4 wheel braking. Unless you go slower on slippery roads, you're only asking for trouble. ...or the rear end of my 4x4, with it's 1/4" thick steel tubing rear bumper, since I will be driving carefully.