'Man, a radiator is little more than a water reservoir'
I don't agree. This IS the principal thermal exchange device designed to cool the engine, and it contains narrow passages that are easily plugged by precipitating sludge or rust particles. If the cooling system has been meticulously maintained since day one, you should never have a problem until it leaks. Normal maintenance is less ideal, and having a radiator rodded out is a very common procedure to rectify this problem.
A somewhat plugged radiator usually can function adequately in normal driving, but can't handle more severe conditions. If the cooling system temperature shoots up to 100C, but tends not to 'overheat', then the radiator is probably not at fault. Look to the systems that regulate the temperature, or for a faulty indicator circuit.