It's not just about tow rating and is a trap many fall into. 1/2 tons can be rated to a pretty decent rating but they still lack things like:
-Heavier frame that can take the stress.
-Heavier axles that can take the stress.
-Bigger brakes that can stop the load.
-Full floating rear end. What's this mean? If you snap your axle the wheel will stay where it belong so you can stop safely. 1/2 tons have a C clip rear end which means if you break your axle (more likely when towing) your wheel and axle can exit the vehicle which is rather problematic.
-Heavier suspension which can better take the stress.
-Beefier transmission that was built to take the stress and heat of towing. Automatics will also be programmed with a different set of shift points and use a different torque converter.
-Believe it or not an engine that was built to tow. Typically if you look at the specs you'll see they are rated at a slightly lower HP than the same engine in a 1/2 ton but with higher torque. Torque is what you want for towing and the difference is usually in the cam used and engine management programming.