On 4wd I'm not a driver but I've spent a lot of time on snowy mountain roads as a passenger, and they're much easier to get out of a drift, and much less likely to skid. It might be true that snow tires are better than 4wd without them, but everybody in a snowy climate has winter tires regardless of what they're driving.  Chains are even better, but they're an absolute pain to be constantly putting on and taking off.