Front and rear drive shafts lock together but the open diffs (or lsd in the back?) makes it act like most 4wd systems ever sold.
Agreed .....except he has the benefit of 'traction control' at low speeds.
The "auto" mode is great when you were driving on paved roads with mixed patches of snow, dry pavement, wet pavement, then more snow/ice/slush again. You still get driven power to the front wheels and significantly increased stability. That probably constitutes 90% of the 'typical' inclement winter driving conditions for the rural and city commuter where the roads are generally kept fairly clean after snows and ice. The last couple years around here (in WI) I can count on 1 hand where we had enough snow to REALLY need the "locked" position. Of course some years there are many more large snows. For those handful of times when it REALLY snows (or if you live in the mountain states), and you're driving in accumulated snow, or ranchers going out to the back 40, 4-lock provides greater stability still. In summer muddy conditions when pulling a trailer up an incline or muddy track locked is definitely the way to go.
I bet the majority of 4x4 vehicle owners (maybe not Ram owners) don't have a clue what the difference is between auto and locked or what axle windup even is, so Auto is a great system, they can set it and forget it. It doesn't really add a ton more wear to the system. Lots of vehicles have awd and go 200k+ miles, including our Jeep which just went over 200k and it's all tight still and a previous Jeep that only needed new front u-joints and driveshaft at about 250k mi. I tore the transfer case apart at close to 300k to have a look maybe install new bearings, but it all looked great inside and I just buttoned it back up and put it back in. I bet Dodge gets a bunch of calls every fall after the first snow, people coming in saying their truck/SUV has a problem and 'feels funny'. Probably why Jeep decided to label their system as Part-time and Full-time so newbie 4x4 owners could keep it straight in their mind (course it confused the heck out of everyone else!).
Mine is like yours and doesn't have the 'auto' mode. Wish it did. If you understand 4wd systems, there's a time and place for it.