For city slickers it's not a must, and most people who buy SUV's don't need it just for snow and ice. I agree with that.
But it's a must for me. I bought my S before AWD was available. In the winter, I put MICHELIN XICE XI3 245/45R19XL on it. They get about the best ratings for a winter tire. But it still gets stuck in my driveway at my lakehouse, just like my Tahoe hybrid does with good winter tires on it until I put it in AWD. I have to put chains on my RWD S to get up my driveway if it gets stuck. Sure, I could leave the vehicle at the top of the driveway, walk down, plow my driveway, and salt and sand it, then drive down, but with AWD I can drive down and up it. I also couldn't go on any roads that are not plowed, salted and sanded if I get RWD on my 3 -- no thanks!
I think people who say these kinds of things only drive on plowed, salted and sanded city streets. Get out in the back country on snow and ice and you need AWD or a tow truck.
So there's no chance my 3 will be RWD like my S. I get the fact that city slickers don't need it. But there's a huge difference when I hit the AWD switch in my Tahoe -- suddenly it's no longer spinning the winter tires but the traction from the additional front tires pulls me out of being stuck. I'll go down my driveway when it's not too bad then spend the weekend at my cabin, when it's snowed while I'm there and if I have my S it's either plowing or chains. With my Tahoe it's the switch of a button. Unless you've actually experienced this, you don't really understand how much of a difference it makes.
Right, and who needs to get a vehicle going in the snow? When I get in mine, after it's been sitting in the snow, I make sure it's already moving...