I think "That 70s Show" -- which I have watched a few times to enjoy its liberal use of marijuana -- is deliberately patterned on "Happy Days." I would guess that the casting of Marion Ross is a sly wink.
Anyway, I'm pretty sure the Happy Days parallels are conscious, channeling and amplifying the same cultural timewarp phenomenon you are pointing out. Calling a show "That 70s Show" certainly suggests the folks behind it are our age and taking their daily irony supplements.
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Hey, remember that -- who was it? Weezer? -- rock video from last year or the year before where the band members are cleverly cut and pasted into Arnold's with the whole Happy Days cast? That was a Spike Jonez joint, the director who went on to delight many of us with Being John Malkovich...
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Did anybody really buy the notion that Fonzie was cool? Didn't we all just find him sadly deluded, a pathetic loser who has to bunk with the ultra-square Cunninghams just so he can seem cool in comparison?