Well, when I had originally made the banner for the Facebook group, it was just the Mane Six. But shortly after I had finished it, Hasbro/Studio B made the change to Derpy in The Last Roundup. So as a show of support for my fellow Bronies in the group (who I thought were overreacting just a little bit), I added in Derpy.
I do agree with you: I don't like how people make such a big deal of her either. Yes, that little change made a lot of the other bronies upset, but in the end, nothing changed. She's still Derpy, she's still in the show and she's still wall-eyed in every other appearance. It was all a huge overreaction.