AND... it was originally intended to be used in a different way than it is now seen used. It originally was NOT designed to be used to open the blade in the same means as a thumb stud.
Originally, spydercos were all metal and somewhat heavy. No plastic or G10 used. The pocket clip was mounted on the pivot pin end of the blade and the knife was clipped blade tip down into the pocket. Using the thumb and index finger, the digits grasp the blade by the hole in the blade, pinching at the thumb hole, finger pad pressed against thumb pad. The knife was pulled from the pocket, and once clear of the pocket the knife was swung point up, and flicked down. The mass of the metal body would cause it to swing open & lock, and the grip was shifted to grasp the body of the knife.
It was later when the plastic was used in place of the all metal knife when the shift was made to carry point up, and the blade rolled out by the thumb only, like thumb stud designs. The original technique did not work well with the lighter materials. There was not enough mass in the body of the knife to reliably open using the index finger and thumb pinch flick. The pocket clip was then mounted at the blade tip end, on the opposite side of the knife, to be carried tip up for easier deployment using the hole in the blade to roll the blade open.
Other knife makers started using thumb studs due to the Spyderco patent on the hole in the blade.
Spyderco trivia!