A lot of people also think that AWD and 4WD are the same thing. They are not. AWD is basically a car that has power to all of the drive wheels. Real 4WD is a cat of a different color. 4WD has totally different gearing, and can (but there is no guarantee will) get you out of situations that will leave an AWD vehicle hopelessly stuck...
While I understand you are trying to say that all AWD/4WD systems are created equal, I think we should leave it at that. Certainly, I do agree that the term AWD has certain implications and 4WD has certain implications, however, I think marketing and public opinion has blurred the definitions so much you cannot make any significant conclusions based on the terms.
It should be noted, that 2WD and FWD could mean ONE or two drive wheels and the the ability to drive the second wheel can vary greatly based on the impliemention.
It should be noted that AWD and 4WD could mean as little as TWO drive wheels (a front and a rear), or three, or four. The ability to drive the different wheels varys greatly based on implemenation.
Even if a AWD or 4WD can drive all four wheels, it may do it differently which may be better suited for different situations.
As suggested, some AWD/4WD systems have the ability to switch into a lower gearing.
And of course, some systems are combinations of the various approaches suggested here.
One thing people overlook is tires. The best AWD/4WD system still touches the road with four small patches of rubber. Tires are a set of compromises, and work better in different conditions. Typically most cars and SUVs have tires ill suited for ice and snow. Tires warrent a lot of consideration IMO.
As Susan points out, even with the best AWD/4WD system (and the best tires) you can't cheat the laws of physics. If something is icy, you can slide right off, despite the best traction. If the snow is too deep, at some point you cannot apply enough force to the ground to move forward no matter what.
There appears to be an interesting theme in this thread where people are thought irrational for preparing "more than considered normal".
People think I'm nuts for having tire chains for both the front and rear of our Jeep, despite having a very good AWD system than can drive all wheels effectively and having good tires.
They'd probably think it even odder that I still assume that I can get stuck.
-john