I went through the first winter (got my 4x4 Compass in december) with the original Firestone all season tires and they were perfect, but they had 0 km, they were perfectly new.
The 4x4 (and all the other traction control gadgets) compensate for pretty much everything if you don't have winter tires. I've had 3, 2x4 vehicles before my Compass and believe me, this is night and day. There's no way a 2x4 vehicle, even with the best winter tires installed would be able to drive like I did this winter.
However, you slide like other cars when you break on a stop sign, 4x4 won't help you there.
However, you understand very fast that all season tires don't have the traction of winter tires when you hear the ABS turning on and off when you break and accelerate and the rev limiter turns on to prevent tire slippage when you accelerate too fast or the ESP blocking one wheel after the other to keep you going straight or to help you negotiate that curve you took too fast.
But hey, all those systems help you correct what you, or your tires can't handle but they have their limitations.
I will buy winter tires this winter but I believe you can do without them if you have 4x4 and brand new all season tires installed, that's what I did.