... actually, if no one minds my getting all psychological up in here, i DO think that the curvy, smooth nature of the art style lends towards the sexuality gleaned from it.
i've seen plenty of behavioral studies which suggest that anything featuring smooth curves or arcs demonstrate femininity, which is perceived as female sexuality in hetero males. even in art class, we were always told that edges and straight lines always implied masculinity and curvaceous forms always implied femininity. (look for those implied lines in marketing sometime -- it is often pretty obvious who marketers are targeting, based on what context + implied lines you see!).
if you look at a pony on the show, edges and straight lines almost don't even exist. their legs don't even have joints. they are unending curvaceous forms. the smallness of them, the bright colors, and the big eyes make them "cute" and child-like, and they don't even have breasts or other human-female features, but the curvaceousness and smoothness DOES imply the female form all over the place. i don't think that was the goal of the artists -- it was probably just what looked the cutest/most modern.
however, interestingly, if you look at a "girl" pony vs. a "boy" pony on the show, on the "boy" ones, you will notice FAR straighter lines and hard edges/corners. It even looks more like they have joints.
anyway it's just kind of my reasoning for WHY a man would become attracted to one of the show's characters. that, and the need to be accepted among his strange internet "clique", after not being able to be accepted by anyone else.
foreveralone + show with gratuitous female form = obsessive sexual fantasies
... so anyway i have spent too long considering bronies and this stupid show so i'm going to go be a normal adult now