I might get a lot of hate for saying this but I think the Derpy page should be renamed "Muffins".

It sounds strange but her cannon name is probably Muffins. In the episode "Slice of Life" the credits call her Muffins. Also, the name Derpy wasn't removed from "The Last Roundup" just because of some angry parents. After some research Amy Keathing Rogers found out that Derpy could mean retarded. Her son is severely disabled so they don't use words like Retard in their house. So she edited her eyes and changed her voice. 

That's why.