The differences between the two trucks are rather dramatic, and more than skin deep. Earlier pickups (and all 4Runners) were made in Japan, while the Tacomas were made in the US. Since the US market doesn't typically see the same abuse as third world countries, changes were made to make the Tacoma more refined and comfortable, but at the cost of overall strength. Some of the differences are:

-Torsion bar front suspension versus coilovers
-Recirculating ball steering box versus rack and pinion
-Fully boxed frame versus partially boxed frame
-12 valve SOHC versus 24 valve DOHC

The rear axles, transmissions, and transfer cases are comparable in strength between the two models. When you get right down to it, they are both Toyotas and more rugged than most of the vehicles you will find on the road or the trail.