A common misconception about standard (not limited slip or locking) differentials is that they drive only one of the two wheels they are connected to. Actually, both wheels are pulling with equal force. Just because a wheel isn't spinning doesn't mean it isn't pulling. The only downside is that, when the traction available to the two wheels is unequal, the tractive effort provided by each wheel is limited by the traction available to the wheel with the least traction.
Limited slip or locking differentials come into play where traction is unequal between the two wheels. The wheel with more traction is able to pull harder than with the standard differential. The wheel with less traction will pull the same as with a standard differential.
I think John Deere correctly calls their tractors 4 wheel drive, at least in the same sense that virtually all other truck and tractor manufacturers have used the term.