The 'REAL' reason why the DVD was recalled, etc.
I have a feeling this topic will become an urban legend eventually but the reality of it all is that Swamp Thing was released in theatres as a PG film. There was no PG-13 (this didn't occur until after Indiana Jones and the Temple of Doom was released in '84) and it wasn't "at the time" deemed necessary for an R rating by the MPAA.
The exact same version was released on DVD by MGM with the exact same rating it had in theatres. A mother who rented the movie for her kids from a blockbuster noticed the explicit scenes and flipped out. She made it her personal mission to get the movie recalled.
MGM pulled the film off the shelf and in part because it hadn't sold all that well in the first place decided not to re-release it as unrated (it was in fact a bargain bin $9.99 dvd to begin with). It can never be released as R because DVD's don't get rated by the MPAA.
In 2005 they released the current version which also sports a PG rating, from what I've read the so-called offensive scenes are still intact and the price is the same. The hype behind the movie being pulled is probably in part why MGM decided it was worth re-releasing. I can almost guarantee though that they didn't spend a second in the editing room for a movie that they're only charging $9.99 for. It's just not cost feasible.