There you go Timbuk. This is a quote from the all knowing one himself
Its legacy......the early distributor based units had a hall sensor in them to trigger the ignition module....as this is effectively cam speed (and on Vx over head cam units it was mounted on the end of the cam)...hence it always was a cam sensor...
For info, the hall effect operates by passing a small current through a slab of silicon from say North to South, as a piece of ferrous material passes, some of the electrons passing through the silicon are dragged to either the East or West side (dependent on direction of rotation), if there is a contact there you get a current flow through it and hence a signal.....
This was pretty evident on the failed cam sensor that Taxi driver sent ....it had a small circuit board with a few capacitors on it which were connected to a 4 contact hall sensor (slab of silicon), in this case both east and west contacts were connected together.