Three Rarity episodes in a row, and Rarity didn't learn a lesson in any of those. First one: Sassy Saddles learned the lesson. Second one: Rainbow Dash. Third one: Applejack and the city ponies (different lessons)
Rarity's episodes did have her engaging with all three different types of ponies. (Unicorns, Pegasi, and Earth ponies, in that order.) So maybe there was a reason? I wouldn't mind if there wasn't. I do love Rarity.