That's not quite true. They've pulled this stunt a few times. Most recently with the 6GB and 3GB versions of the 1060. That was arguably even worse because they did it after the launch.
https://en.wikipedia.org/wiki/List_of_Nvidia_graphics_proces...
Looks like there's also a 5GB version which has slower clocks... which is about 10% worse... but I assume that's mainly due to clock rate, not the memory or the actual silicon.
Those all have the same amount of CUDA cores and processing pipeline, though. Unlike this '4080 12GB'.
See: https://www.videocardbenchmark.net/compare/GeForce-GTX-1060-...