This seems to be a similar situation to that one time where a parent was extremely offended by Portal 2 poking fun at orphans. Sure it wasn't exactly right to do so but the game developers obviously don't have a grudge against orphans or had any intention to hurt their feelings. It was just used as a joke, which is exactly what is happening here. Derpy is not at all an offensive name. I have an autistic brother who watches the show, when I asked him if he though it was offensive, he was baffled that I asked. "Of course not" he said, "why on Earth would be offended by THAT?". To top this all off, lets have Steve Hughes talking about being "offended":
^ That right there pretty much sums up my feelings for this.