^ I suspect this is the truth. What people often forget is that film was, before the advent of home video, a transient medium, one that was enjoyed for two hours and then forgotten, unless you made multiple trips to the cinema. It wasn't like television, where there were always reruns. And there was, of course, anything up to two or three years between sequels. Nobody was expected to remember the fine details for that long. It's for the same reason that Superman II using Kal-El's mother in the fortress of solitude scenes, repeating word-for-word dialogue said by Jor-El in the original movie, didn't actually matter at the time. Nor Carol Marcus' absence from the Genesis tape footage in ST III for that matter, or Jennifer being recast in Back To The Future II. Nobody was expected to remember small details like that back then. It really only stands out today because we've got used to being able to watch movies back-to-back in the comfort of our armchairs.
Actually, ALL of those instances you mention were enormously annoying back then. Carol's absence was known well in advance, as was the Elizabeth Shue replacing thing, but that didn't make it any better. If you really want to cite SUPE 2 though, cite how they've got some joker doing a Gene Hackman impression through most of it, because Hackman wouldn't come back and loop his lines for the new director (though I admit I didn't know the reason for the weird voice till a couple years late ,it was annoying as hell.) Maybe it is because attention spans ain't what they used to be that this notion of your came to be. Pre-internet and pre-DVD and pre-laserdisc and pre-VHS, people were still audio taping movies and buying the scripts if they wanted specific enhancement beyond what they saw in the theater.
Novelizations and published versions of the script used to be so much more important in the days before we could own movies in our own collections. My point was, people might still have found those things annoying at the time, but the studios themselves weren't quite as fussy about whether continuity matched exactly from sequel to sequel. I'd expect them to care about it a great deal more now, because they'd know that we're all going to be rewatching the movies multiple times (and, often, in close proximity to each other - no two or three year gaps between release dates). Though to be completely fair on Back To The Future in particular, Zemeckis, Gale and co did an absolutely astounding job of matching up all those 1955 scenes with the ones we'd seen in the first movie. On the whole their continuity was spot on, possibly a stand out compared to most movie sequels (home video was very much a factor by 1989, of course).
We do however know from TNG that a torpedeo casing can be sed as a Transport of sorts (TNG: "The Emissary") now perhaps when they where designing it, they designed that in incase it was ever needed.
It's just a movie, a science fiction/fantasy one at that. Suspension of belief of certain things is simply required to enjoy it.
I don't think it should be as important to people now as it seems to be. After all, these are stories meant for entertainment, not historical documents.
I agree. Fans DO take continuity far more seriously now than we used to. Using my own experience for example, I remember when Star Trek III was new and I first saw Spock's tube on the surface, I DID remember thinking, "hey, that looks different from what we saw in II.", but then, I also thought, "well, it probably took a few weeks for the GRISSOM to get to the planet, and what with weather and all...." The thought took about three seconds. Then I went on with watching the movie. And let it go at that.