[Phil G4SPZ]

You're right there. All our 'sensors' have evolved to work by quantizing the inputs to a level of resolution that's adequate. The result appears analogue because the granularity is so small. 'Modern' technologies like film, TV and audio all exploit the weaknesses in our senses so that we don't notice the missing information in MP3 audio coding, for example, or we see a sequence of still images 25 times a second as a continuous moving image.

It strikes me that most 'analogue' electronic systems also have limits to their resolution, such as the uniformity of density of magnetic particles on tape or (as you discussed) grains of silver on film. As long as the granularity exceeds that of our ears or eyes, all looks and sounds fine! When imperfections such as noise, limited frequency response and so on exceed a certain low level, we start to notice them.