When I was young, "Made in Japan" carried the same overtones as "Made in China" does now. It was inaccurate, or at least incomplete, even then; Nikon's S2 camera, for instance, was no slouch. But a lot of junk got produced in Japan (although, to be fair, a lot of junk back then got produced in the U.S. too, but somehow that didn't get attention).
But Japanese industry long ago made the decision to focus on quality products, so I'm not surprised those sockets are quality.