Actually, I don't think that skyman's argument is entirely without merit. Planet of the Apes (1968) is rated G and features nudity and swearing; Jaws almost certainly would get a PG-13 today; GL had THX-1138 re-rated and got an R for his director's cut. The 1997 board was definitely more conservative than the 1977 board, and GL may have done it as a pre-emptive strike.
As for Spielberg and the guns vs. walkie talkies, terrorist vs. hippie, etc., none of those changes would have changed the rating.