In the photography world, I am almost 100% wet photography, but in my
professional life, I am an engineer with a background in the design
and use of A/D converters.

It seems to me that there is a big technical difference between
colour and black and white material when scanning - and that is
because with the way the dyes work in transparancy material they
behave much more like a continuous image, and you would need an A/D
converter with resolution similar to what the transparancy supports.
If you look at a b&w negative under a microscope (the way the scanner
sees it when scanning), you don't see levels of gray, you see grains
which are black, on a white background, and the overall density in an
area is determined by the percentage of that area which is covered in
grains.  To digitize this you have two options - one would be to use a
sensor in the scanner which is significantly larger than the grain
pattern, and use the A/D to average this out - the result would be an
image in which you lose spatial resolution (edges would not be as
sharp), the other alternative, and the one which I would chose if I
were serious about this is to use a very small sensor (very high
number of DPI) and a low resolution A/D converter.

To achieve a scan with no loss of data there is a theory that tells
how small the sensor spot has to be (about half the size of the
grain).  Most scanners that boast very high resolution (DPI) are
actually interpolating between actual samples, their ability to
resolve black lines is significantly lower.  The specification which
is really needed is not one of the things that scanner manufacturers
publish.  In this case the resolution of the A/D converter is almost
irrelevant.

If you were to do a scan in this way, and then generated a digital
print from it, enlarging it a lot, what you would see would be the
same sort of graininess that we get in the darkroom.

The previous poster mentioned the use of a variable gain amplifier
(VGA) prior to the A/D to expand/compress the range of the scanner.
This is done, but a more common use for the VGA is to use it to
compensate for non-uniformity in the illumination intensity.  During a
calibration cycle, the scanner measures the bulb intensity and saves
it, then during the scan it alters the A/D sensitivity to compensate
for bright and dark areas. - A dandy technique, but really only
valuable when scanning colour materials.