I would imagine the whole Moon landing proximity was a big deal to kids at the time...That whole thing would've been entrenched in the imagination then whereas it's a bit blase to us lot...People were actually still going to the moon in the 70s for a start.
And you know, it's not an awful film, the set and costume design is fantastic for instance. Very iconic, original and easily referenceable.
I'd put it partly down to originality, partly down to the merchandising and the "must have" mentality that went with that, and partly something to do with being a rather care free, modern, non-war generation, at the beginning of the age of consumerism...Or something. I'm just sort of making that up. Fads and obsessions are common place now. LoTR, Avatar, The Nolan batman stuff...People get very obsessive over it...And as one of the very first, Star Wars has maintained it's hold over many of those who got caught up in it.
But (back to the point) it's for these people Lucas keeps releasing and fiddling with stuff...Cos it's these people who keep buying it. My god daughter sure as hell doesn't want a Star Wars DVD, and neither do I.