HairMetalLives,
You are correct in saying that since the early 90's Season 1 episodes would never air with the original opening and would be replaced with a different opener from the later seasons depending on which station would air the reruns. When TNT aired them in late 1991/1992 most would be Season 5 openings, for instance I remember the Paul Williams episode beginning with the opening from the Senor Wences episodes. Later in 1994 when Nickelodeon aired the shows the Paul Williams episode would have the opening from the Milton Berle episode. Then in 1999 most season ones would have the Milton Berle opening where Gonzo's horn squirts water. I'm not sure how they decided which opening to use over the originals, but the theory behind it is that the general public, rather than the real die hard fans, are only really familiar with the opening with the arches used from Season 2 onwards. Therefore when the shows air out of sequence on Nickelodeon, TNT, etc., it gave it more continuity if they all used the same opening. I felt it unnecessary, fortunately which the DVD release of Season 1 all first 24 episodes are preserved with the original opening (despite the several edits due to music licensing, etc. Jim Nabors singing Gone With the Wind, All of Me from the Paul Williams episode, Charles Aznavour singing Dance the Old Fashioned Way, and Vincent Price singing You've Got a Friend with the monsters). Hope that answers your question.