All true. And perhaps instructive...

Roman war chariots were set to 4 feet 8.5 inches wheel spacing for a good reason, and that reason, for the most part, still applied to horse-drawn vehicles right up until mechanisation did away with horses. Up to that point, there was good reason not to change the standard, and no good reason to change it.

Even on the early plateways, even with mechanical locomotion, there was still good reason to keep the old gauge—the jigs were already available to make the wagons (and the wagons were originally horse-drawn models anyway), and no really good reason to change it. (One should note that these early plateways had the flange on the rail rather than the wheel, so the wagons could run both on roads and on the plateways.)

Up until railways were invented, wagons were mounted between their wheels, partly for stability but mostly because large wheels are better able to negotiate bumps in roads. Early railway wagons, although given smaller wheels, were still mounted between the wheels. Steam locomotion however meant that larger loads could be pulled, and increasing the capacity of wagons became important. For a while no-one wanted to build rolling stock that was too wide for fear of having it overbalance. Instead, broad gauges were used, up to 7 feet.

Broad gauges soon proved to have limitations in cornering at any kind of speed, so the problem of overbalancing carriages was revisited, and it was found that the narrower "standard" gauge could be used, with a decently wide carriage, and it still didn't matter if everyone sat on the same side of the carriage because the centre of gravity didn't move outside the wheels. Narrower gauges still could be used, at the expense of less stable rolling stock—this was frequently done in hilly places where bends needed to be tight to negotiate tricky country.

In the end, standard gauge—4 feet 8.5 inches—prevailed, simply because the alternatives, all the way down the ages, have not provided sufficient reason to change.

This, I believe, is something the IPv6 folks need to consider.

Don Stokes, Network Manager, Victoria University of Wellington, New Zealand.