I'm a little hazy on the order here, but i think what got me interested in playing D&D was playing D&D. We were on a family vacation, and visiting friends of my folks who had kids around our age. One evening, one of them ran my brother and i through a short adventure. The horn of bubbles has been perhaps my favorite magic item ever since.
Anyway, i loved it, but didn't really know what to do next. I bought the D&D Basic Set by mistake when i was trying to buy Dungeon!, but i can't remember whether i'd already had it at that point, or i got it after that first game. I do know that when i first tried to read the Basic Set, i got sorta overwhelmed by the complexity, and invented my own game instead (which, logically enough, turned out to be far more complex and arbitrary). It was a fair bit later (at least 6mo) when i finally sat down and read it and made some sense of it. That, and played for a while with my best friend as DM--he'd learned from a mutual friend who's older brother gamed.
Also, i was big into the Choose Your Own Adventure (and a couple other brands of the same thing) at around that time (can't remember if i discovered them or D&D first), and have always been a huge fan of both folklore/mythology and scifi/fantasy. But i don't recall making any sort of logical connection between those activities and D&D at the time, and certainly didn't seek out D&D because it was like any of teh above--i had never heard of it until i played it.
But, in short, i got into RPGs because they're RPGs, not because they're like any other activity, or share common elements with other media. Which makes perfect sense to me--IME, the only activity that is sufficiently like RPing to usefully predict interest in RPGs is collaborative storytelling--and that just barely--and that's hardly a common hobby/pasttime. IME, those who try RPGs because they're like computer games are usually disappointed, and go back to the computer (as opposed to those who try them because they're unlike computer games, in some crucial way that they expect to be an improvement). Likewise, plenty of people have a huge interest in spec fic, but have no interest in "living" it, so assuming a fantasy fan will like RPGs is, IMHO, silly. And so on for actors, fanfic writers, wargamers, etc. Likewise, i've known a fair number of RPers who can't stand fantasy/scifi lit/TV, aren't really into computer games, etc. (And, yes, at least one of these was a big fan of playing fantasy RPGs--just didn't like being the oblserver, i guess.) RPGs are a fairly distinct breed, and i've yet to stumble on to a predictive correlation between other interests and them. Which makes me think that a survey like this is going to show you correlations, at best, not causation--you can't say "a ha!, 25% of responding RPers attribute their initial exposure to D&D to computer games, therefore computer gamers are likely to like RPGs".
