DH tells me that the bullion knot is not merely an embroidery stitch, but is a "unilateral binary" stitch. Boolean logic uses binary numbers, and is the basis of modern electronics. According to DH, without Boolean logic, there would be no iPod. Scary thought. Considering the wraps of the bullion knot form little zeros and the thread it's wrapped around forms a horizontal "one," I guess I get the theoretical mathematics/needlepoint connection.
I had hoped to find some information on the bullion knot's background, but no such luck. Sharon B's Dictionary of Stitches lists some alternate names for this stitch - bullion stitch, caterpillar stitch, coil stitch, grub knot, knot stitch, post stitch, worm stitch, and my favorite, Porto Rico rose. Bullion knots make lovely embroidered roses, although I haven't attempted one yet. Some of these names are obvious - these knots can look like tiny caterpillars - but I'm wondering if the name "bullion" comes from the stitch's similarity to gold bullion when worked in gold, or if it has something to do with the tassels used on military epaulettes.