AWD is not intended for off-road as much as tougher on road conditions. It is also for helpful on winter days and makes driving much easier. There is a little penalty in fuel on modern vehicles (usually 1MPG).
Is it necessary, no. I will state The VW Routan/Dodge Caravan(close cousin) however are not at great handling winter conditions on the stock all-seasons. I would give them a poor especially if loaded up given my experience with relatives vans.
Like another poster stated adding winter tires is the safest thing on ice & snow by a far margin coupled to common sense.