Tom, in my opinion you are correct to question this ptractice.
There is no point in pumping grease into the same place via two different zerks.
David Rutherford always recommended using EP90 or similar for the top of the kingpin. The stub axle and kingpin oil-way act as an oil chamber and the grease acts as both lubricant to the kingpin bushes and to contain the oil.
The grease gets wiped off by the vertical motion. The oil bleeds out to maintain lubrication.
