From my perspective it's never been a "kid's show," and I seldom think of things in those terms. Just like I haven't thought of it as a show for little girls, despite recognizing that they are the target and that most of society would perceive it as such. The morals and lessons presented are equally applicable to everyone's lives regardless of age or gender, and were presented in such a way that the children could understand without the adults feeling patronized. I felt both enriched and entertained despite being a 23 year-old guy when I discovered MLP.
From a business perspective, however, it really is a kids' show, even today. The majority of merchandise is that frilly, pink, cheerful stuff you find in Target, and the advertisements and commercials typically appeal to people who love that sort of thing (small children).
Hot Topic is a dark place overall so they won't carry a line of merchandise that appears overly cheerful. As for why you're seeing what one might consider more "adult" merchandise in stores not frequented by children, I think that might have just as much if not more to do with them trying to milk those kids growing out of the target demographic than appeal to adults bronies. Keep in mind that this show is pushing four years now. Almost half of a decade. They need to make sure this money maker stays relevant as long as possible to the naturally shifting interests of aging kids. Items for display rather than play, posters, earbuds, and movies about high school drama (Equestria Girls) appeal to their sensibilities more than the talking Pinkie in a diaper that did several years back. They're keeping with the times. Smart move on their part, but we're still a peripheral concern. Adults are too critical and fickle. I've yet to hear a child or tween complain much about show accuracy in the toys for which they're begging their parents to pony up some cash.
Understood and somewhat agreed, but most of such claims I've heard have been facetious. Jokes made by guys to satirize themselves. I try not to take it too seriously when I hear men say stuff like that.