I'm also a member of an Audi forum. Some people over there just don't get it Though this year they don't seem as bad, maybe that is because of this weather.
They usually revert to saying something like, "the best option is both." Referring to quattro and winter tyres.
Perhaps someone here can enlighten me, as I do not understand this: If I have winter tyres on my car, why exactly would I need 4WD?
You obviously think winter tyres are some sort of fantastic thing that can cope with anything.
Friend of mine couldn't get up his road on Sunday or Monday in his A4 with winter tyres. He jumped into his wife's 80 Quattro with summer tyres, locked the diff drove up road.
Winter tires are indeed a fantastic thing as they provide the needed extra grip under all phases of driving (set-off, corner, brake) on all 4 wheels on any car. AWD is just splitting the load (torque) on 4 wheels in an effort to reduce each wheel's spin but also reach a minimum enough grip to get you going but that's pretty much it. It offers minimal benefit in cornering and none in braking on a slippery surface as the last, most important factor which is the friction between road and tire is compromised with a summer tire. If you happen to be just inside that traction range, usually in the case of fresh shallow snow, then you might mistakenly think AWD is a winter tire alternative...
That been said, it's still easy (if you wish so) to provoke wheel-spin on any car even with winters on, 2WD or 4WD, no surprise there. It might seem so but a winter tire is not actual magic so it still has its grip limits. It's just that those limits are raised (compared to a summer tire) to make the car drive-able and safe, you still need to exercise caution when driving in bad conditions.
Your friend's story proves that he probably has little patience and a heavy foot (bad combo for winter), and certainly not any AWD superiority over winter tire compound, that would be insane even to be implied, especially in a car forum. Also, a snowy road might mean many different things from being able to move on summers with enough throttle modulation to even cars with winters sliding off. There are many variables that are over-looked when someone tells an interesting story about what he achieved in snow with summer tires.
Perhaps someone here can enlighten me, as I do not understand this: If I have winter tyres on my car, why exactly would I need 4WD?
Setting off at ice or driving up very steep uphills, you would get the benefit of some extra traction. If we are talking a combination of the worst conditions (super slippery surface and significant inclination) it might be just that extra bit of traction you need to get going. However if you are in such a situation that you do need that extra bit of traction, then you'd absolutely need winter tires already to turn and stop no matter what car you're into.
The bottom line here I think should be that AWD is a supplement to winter tires and not the other way round.