"You are right....these things can't be blurred - one pixel on the render can't get material room info on another pixel (not through nodes anyway)." That's a feature (!) of the REYES rendering algorithm (the one that FireFly, PRMan or 3Delight are based on). The benefit is that since no shading point depends on other shading points, they can be calculated in parallel on vector computers or SIMD instruction sets and that the renderer can discard things it already rendered from memory (because it won't need them again).