That may be in terms of a video demonstration, but it also would have disenfranchised the user from the experience. Having the demo on the Mac actively engages the user, which Jobs knew was key to marketing any new product. Also, most people I know toss such things aside as a video has nothing to do with the product you're unpacking. And, the computer was not likely to be in the same room as the TV. In 1984 we had one TV. so consumers would be trotting off tot he TV and VCR, taking them away from the computer.
As for longevity? I totally disagree. The spinning head on the VCR is hell on magnetic tape. It's also much thinner than the average 60 min. cassette tape, making it much more venerable to being eaten by all the spinning capstans and heads than the single one in a cassette deck. There is also much more audio information proportionately encoded on a cassette tape than on a video tape. So with normal degradation the audio will be much better on a 25 year old audio cassette than a VHS tape, but the picture will be much worse, making the experience today much more vivid with a real Mac, and slightly degraded audio, than a grainy video tape on antiquated equipment - I don't know anybody who still owns a VCR, but I do know a few people who still have cassette decks. Then there's my own experience. I still have cassette tapes from 1982 that sound great. VHS tapes from 1989 look and sound terrible. Even movies I bought. In addition, I probably only had about 4-6 cassette tapes over my life eaten by tape decks. I have lost over a dozen VHS tapes to VCRs in the 15 years I used them, mainly in the early days when they were cutting corners to sell them for less. The problem was made worse, because renting all those tapes that had been in so many other machines, actually increased the risk of tapes being eaten due to dirt buildup and previously damaged tapes spoiling the delicate alignment. Remember the tracking adjustment knob!? LOL So under the circumstances, I think the audio tape was the correct solution. Plus, that was a fairly common instructional method in those days. There were even instructional LPs in the 70s, so people would not have found this unusual. By the time VCRs might have made sense, at least economically, the Mac was capable of running A/V demos, and thats the directional Apple chose, which kept them user experience directly connected to the Mac.