Radiosity is not ray-tacing per se and for real-time applications it is still "faked" to a certain degree. Also, the accuracy is not true to real world lighting.
The idea behind ray tracing is that the end effect is so close to real world lighting that nothing can tell as it actually simulates photons. Radiosity is a clever trick that simulates ray-tracing to a degree, but in the end is still a trick. It is, however, a great leap forward in photo-realistic lighting. Much the way that Specular, Ambient and Diffuse were when they game out (instead of using pre-rendered light maps)