My partner and I were just speculating last night... if ponies really were "sexless" cartoon characters, that is they didn't have genitals, then (disregarding Faust's "the usual way" comment) how would they have sex/reproduce? The answer: they would rub all four hooves together! That's something ponies wouldn't usually do! So when this picture showed up in the drawfriend on EQD I had to show her, and she said "they're totally doin' it!". We had a laugh.
It's all speculation right? They are pretend after all.