I remember reading that issue when it was new. I would have been 9 years old.
I think all of the references to AT-ATs and Star Wars are telling. Dragon's audience in 1984 (without checking my files I'd say somewhere at about 100,000--twice the current size) had a lot more 9-year-olds in it than it does today.
Obviously, the audience for D&D did too. 9-year-olds didn't just stop reading Dragon--they stopped playing D&D, period.
I think the best--really the only--explanation for this is that D&D has lacked a credible "entry-level" product for the game since at least the beginning of second edition and the end of the "Basic Set" era. That kept the game out of toystores (where I bought most of my D&D stuff in the early 80s), and thus out of the sight and minds of kids.
The "kid" players of D&D's first wave have grown up to be the editors-in-chief of the game's magazines, the heads of its design departments, its greatest artists and writers, and its most reliable customers. D&D, as a brand and as a social institution, is currently benefiting greatly from the wave of kids who were attracted to its first wave. The lack of credible youth-recruiting in the tabletop RPG hobby in the last 20 years will soon come home to roost, to no one's benefit.
Lots of kids still play the game, of course, but Dragon doesn't get very many of those letters, anymore.
--Erik