My GUESS as to why Intamin uses the little drain conductor and the other manufacturers did not is that Intamin uses non-contact magnetic brakes to slow the train, and a rubber tire on an advancing motor to stop it. All of the Cedar Point coasters from other manufacturers use friction brakes with a metal lining. So as soon as the brake contacts the train, any charge built up in the train gets conducted to ground through the brake caliper. On the wood coasters, of course, there isn't any polyurethane or Fiberglas to generate a static charge, and the steel wheels and steel rails are all grounded anyway.
It is kind of interesting that because of the polyurethane wheels, most steel coasters are electrically "floating" most of the time. We don't notice the charge build up when we ride because we are at the same potential as the train, and when the train's charge drains off into the brakes, we don't feel anything (again, we stay at train potential) and when we get off the train we don't get a "poke" when we get back on solid ground. A great example of this was the Zierer kiddie coaster at Geauga Lake. Six Flags equipped the ride with mats on the ground on either side of the track...not because the ground wasn't soft enough to hit with your fingers, but because the mats were non-conductive and could prevent riders from getting unpleasant static shocks.
