Yep.  As it happens, there's a full-blown article about it in this month's
Scientific American (he says disgustedly -- talk about going to the dogs).

david

At 20:44 5/3/2000, Nicholas Wilson wrote:
>I believe auto shutoff fuel nozzles work by a slight suction created by a
>Venturi that the fuel jets through inside the valve assembly. On the lower
>surface of the fuel nozzle near the tip there is a small port connected to
>a tube that runs inside the nozzle up to the valve assembly. Air is sucked
>in through that port to relieve the vacuum until fuel or foam reaches it.
>Then the unrelieved vacuum moves a diaphragm inside the nozzle and trips
>the fuel cutoff.

David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"