Pinkie Pie as Pegasus

Lauren Faust has donated sketches from her original pitch of My Little Pony: Friendship is Magic to help raise money to help Japan, revealing that Pinkie Pie was originally going to be a pegasus.  This explains so much, really, about Pinkie Pie's character, such as why she's always popping up in odd places.  If Hasbro had let Pinkie Pie stay a pegasus, Fluttershy would have been an earth pony, which explains why she's the odd duck pegasus who prefers to stay on the ground and care for the forest animals.
This also explains why Pinkie Pie had wings in one image from the licensing style guide: