Something that seems to have been critically overlooked in this thread is that anime is not only popular with boys, but also with girls. Seriously. I mean, you can be wandering through the video store and watch teenage girls converge on the anime section (or on the manga book rack nearby), looking for the latest release of one of the series targeted at — you guessed it — young female viewers and readers. Sure, you have creepy guys watching Sailor Moon because they like the thought of schoolgirls in short skirts, but the show itself wasn't aimed at that demographic, even by the Western studios that imported and translated it.
Because comic books and animation just plain aren't seen as "kids only" stuff in Japan, manga and anime as media are able to explore genre combinations (and turn a huge profit!) that the average American would never think of as appropriate subject material for a "cartoon." This is probably why some of the most infamous stuff is the pornographic material — it had early market penetration in the US, was unlike most anything America was offering at the time, and was certainly memorable. To some people, though, their first exposure to the stuff formed a first impression they could never get past — "Anime? Oh yeah, that pervert stuff from Japan." It's understandable how a person could get to thinking that way, particularly as the sort of bootleg dealers that hang out at conventions prefer to show the hardcore stuff, but I imagine it became quite a surprise once the other genres started filtering into our video stores.
I don't think you can cite any one particular reason as why anime has gotten as popular as it is —_some aspects sell to the nostalgic folks who discovered this in their youth (Robotech), some to young kids who like the shows and their tie-in products (Pokemon and Yu-Gi-Oh), some to teenage girls who like being targeted with romantic fantasy in settings more outlandish than Hollywood is willing to chance (Fushigi Yugi), some to younger boys who like over-the-top battles (Dragonball). The hardcore anime buffs may appreciate multiple genres for all of the above reasons, but I don't think there are that many people who thinks that all anime is great just because it's anime. I mean, do you honestly know anyone who thinks that all American comic books are great just because they're American comic books?
Studios and TV networks like it, though; it's a lot cheaper to obtain the rights to an anime show and pay for translation and dubbing than it is to fund a show that's animated from scratch. So expect the trend of importing to continue; it's pretty durn profitable if you can find the right show.
