Limited slip diffs are usually fairly loose. They need to slip during turns (outside wheel turns faster than the inside), so they can only apply a limited amount of power. I don't know if his has LSD, but it really didn't matter. His rear diff was sitting on a high spot. He was done at that point. Both front wheels were on solid enough ground to have pulled him out if he had 4WD.

You are correct about 4WD not really being 4WD. Even if he had 4WD and only put the tires on one side of the truck into a rut or loose mud, he would have been stuck. It wouldn't matter that the tires on the opposite side could have been on dry ground. Had a friend get his Jeep stuck like that. Rather embarrassing!

His was an earlier version. However, the new Xterras have ABLS (Active Brake Limited Slip) on the front AND rear axles. The brake is automatically pulsed on a spinning wheel(s) to transfer power to the other wheel. This keeps power to the wheels that have traction. Not a true locker front and rear, but mimics it, at no extra cost. I'm very impressed with ABLS so far.

In his case, only having 2WD and being high centered on the rear diff, ABLS wouldn't have helped. He needed to be dragged off the high spot, either with a 4WD front axle (if he had one), or by a buddy.