This debate will go on for ever. I see exactly what Rob and 306maxi are saying, its proven due to the tyre materials, having said that, in all my years of driving and riding motorbikes, I have never used winter rubber.
I just drive to the conditions, if anything it makes me more wary and aware of the road limitations and my own, god forgive me for standing on the same side of the fence as Draigflag but I cant honestly imagine the need for winter rubber, even knowing that the all weather tyres wont be as sticky at sub 7 degrees....
But fair play to those who do it, it does make sense but not for me... I couldnt justify the space for 4 wheels and tyres for half a year degrading in the garage. If ever I did, the winter rubber would HAVE to be on alloys... more expense... and TBH I dont recall getting into any "out of control" situations with my all year round budget rubber.
I'll close the door on my way out...