Looking something up in the oldest 4WD book I own, the 1970 Four Wheel Drive Handbook by James Crow and Cameron Warren (there's more about the book here), I rediscovered a description of why automatics are better off road. Four decades later, the advice remains sound and worth repeating for those who still think you can't beat a manual.
"We’d say that if an automatic transmission is available for the model you’ve selected, get it. Not that we’re lazy. Not that we both didn’t grow up on stick shifts and know how to use them. Not that we believe in spending money unnecessarily. We say get your 4WD with automatic if you can because it’s better for off road use. Automatics consist of a torque converter and a planetary gearbox. For 4WD purposes, the torque converter is what’s important. This is, in effect, a pair of turbine blades, one of which is attached to the output shaft of the gearbox, the other to the driveshaft, and enclosed in an oil-filled case. When you step on the accelerator, the engine speeds up, the output turbine speeds up and the motion is transferred by the oil to the turbine that turns the driveshaft. It’s like putting one electric fan in front of another, then turning one of them on. The air blown by the turned-on fan makes the blades of the second one go around. Do you begin to see why we like the torque converter feature? It’s because you can deliver just enough power to turn the wheels without breaking traction. With conventional drive, the only way you can deliver less torque to the driveshaft than comes off the flywheel is by slipping the clutch, and that’s a poor practice to have to engage in. When you’re in sand with an automatic, you’re far less likely to dig in because of wheelspin; you simply mash on the accelerator with a gently increasing pressure (to multiply the torque) and munch ahead. With a manual, you let out on the clutch, feed on the gas at the same time and hope for the best. An automatic is better."