The holes are only for manufacturability.

Americans plugs are very strange

I’m not American, but I’ve lived a few years in the US. I find it very interesting that the US invented the electric infrastructure that we use today, but they really screwed up a few things. Firstly, the connectors are far too unsafe. They are flimsy and have no protection from electrocution. Secondly, by using 120V as the main voltage, you need more current to do the same amount of work as a 240V system. Thay means thicker wires, more stress on the plugs, and greater fire hazards.

Shuko plugs FTW