The rating PG had a different implication back in the 80s. PG then is PG-13 now. I believe it was Indiana Jones and the Temple of Doom that caused a moral outrage at being 'only PG' that it pushed the MPA to disambiguate between PG and R. To be fair, Indiana Jones came out in '84, and Space Balls was '87, but obviously this change didn't really come into effect until the late 80s to the early 90s.
So don't go blaming contemporary websites, blame Steven Spielberg.