The difference is, those characters were always...less than bright. But with Ditzy, she used to be normal until people found that split second of derpy eyes. Then they started calling a perfectly normal pony 'derpy' and treated her like an idiot.
Also, I think you are very clearly missing the point of this. This has nothing to do with mental disabilities, this has to do with the fans heartlessly teasing poor Ditzy just because of one picture. How can you love and tolerate when you make fun of a pony and call them names just because they had a bad picture of them taken?
Anyway, to SrFrog, that is true, and she is adorable, AND I'm glad she is getting airtime. But I just can't feel good with the way she has been treated. But what about that one blue pony that lost his nose, had one eye, and a line going across his head, making him resemble a pokeball or Portal GlaDOS core? He looked far worse than Ditzy and probably had as much airtime as the derpy eyes. But for some reason it was poor Ditzy that was teased and called names
If you honestly think this is about being mentally handicapped, please leave until you actually understand the topic. And in response, who got teased more? Twilights full episode of being insane or a split second of derpy eyes? Is Twilight's character going to change over that episode? I highly doubt it.And I can say the same to you. "You and people like you are the only ones who think teasing someone just because of a bad picture is ok"