(Also, since when can the side of a paper clip cut masking tape? They should have used some sort of exacto-knife from the manager's office.)
I just tried it with a paper clip and a cardboard box that was still sealed on the bottom with clear packing tape, and it was just as easy as shown. Once you pierce the plastic with the tip of the paper clip, it slices through the tape quite easily.
I think that packing tape of this sort is designed to be easy to pierce and tear. You want it to be able to hold together against shear forces and the like, so the box won't come apart, but you also want people to be able to open their packages without too much difficulty.