I just opened up the garbage disposal switch in my condo built in 1977 in the US. I believe this is the original switch, and therefore I will be replacing it right away with a new switch that has a ground screw. And of course, I will connect the grounding wire (see photo) to the ground screw. I consider it odd that the building has grounding wire, but that the switch has no ground screw. I have already replaced four light switches that had no ground screw in my condo.This is what begs the question.
Technically it happened about the same time that UL started listing non-metallic boxes for residential use. When the boxes ("handy" boxes) were steel, any device body was grounded by virtue of the mounting screws. Once the boxes became non-conductive, the devices that REQUIRED grounding needed to have grounding screws. When I started as an electrician in the mid 70s, the code stated that for metallic boxes, you had to ground to the box but for non-metallic boxes (at that time they were still "bakelite"), you had to ground devices that "required grounding". That is still the way it reads to this day (250.148).
"One or more equipment grounding conductors brought into a nonmetallic outlet box shall be arranged such that a connection can be made to any fitting or device in that box requiring grounding."
The tricky part was, when did switches start "requiring" a grounding screw? That changed only when UL started requiring ground screws on switches, some time around 2010. When there was no ground screw, there was no "required" grounding.