On the contrary.....tie plates were rarely ever used in narrow gauge construction. It was felt at the time that the lighter weight of the equipment made them unnecessary. This was one of many factors that allowed narrow gauge railroads to be built for only a fraction of the cost incurred by standard gauge construction - along with smaller equipment, lighter bridges, reduced excavation, etc. Unfortunately for narrow-gauge advocates, this cheap construction ultimately led to higher maintenance & operating costs which, along with the high cost of freight transfer, rendered most narrow gauge railroads uneconomical. The Florence & Cripple Creek RR in Colorado was thought at the time of construction to be one of the most sturdily built narrow gauges, and recieved special press mention of their use of tie plates - one of very few to do so. Perusal of the many picture archives of the Rio Grande Southern reveal that even up to the end of operation in the 1950's a good bit of the line was laid sans tie plates.

It was not only narrow gauges that did this; some lightly-built standard gauge shortlines and interurbans did so too. The Union Railroad of Oregon, originally built as a light-duty "dummy line" was one such. When I first saw this line in the 1970's it still had the original (very light) rail, probably 45 - or 56#, and no tie plates. In places the rail had sunk nearly to the head into the ties. The URRO's lightweight Plymouth locomotive could apparently still negotiate the line, but Union Pacific had threatened to disallow interchange of any UP rolling stock because of the potential for derailments & equipment damage. In the last few years before its demise the URRO (which was less than three miles long) did re-lay its mainline with 85# rail and tie plates so that it could continue interchange.
J