Your first link doesn't seem to be about introducing noise, but removing it by averaging the value of multiple captures. The second is to mask quantizer-correlated noise in audio, which I'd compare to spatial masking of banding artifacts in video.
Noise is reduced to make the frame more compressible. This reduces the resolution of the original only because it inevitably removes some of the signal that can't be differentiated from noise. But even after noise reduction, successive frames of a still scene retain some frame-to-frame variance, unless the noise removal is too aggressive. When you play back that sequence of noise-reduced frames you still get a temporal dithering effect.
Noise is reduced to make the frame more compressible. This reduces the resolution of the original only because it inevitably removes some of the signal that can't be differentiated from noise. But even after noise reduction, successive frames of a still scene retain some frame-to-frame variance, unless the noise removal is too aggressive. When you play back that sequence of noise-reduced frames you still get a temporal dithering effect.