I guarantee you that Akira Toriyama forgot all about that by the time that Goku arrived to face Nappa. While Piccolo, Tenshinhan, Yamucha, and Chiaotzu were strong, I'd assume that they'd at least make some sort of comment that the gravity feels off on King Kai's planet (especially since Goku really felt the strain setting the gravity machine to 20x in the spaceship, and he was much stronger than they were).
I'm betting Akira Toriyama simply forgot about that because -- like all things that were conveniently forgotten -- it no longer served any purpose for the story.