Something else to consider, along the lines of the Tragedy of Pinkie...
There's a lot of speculation among the fan community, and quite a bit of evidence to support it, that Equestria used to be a cast based society. The Alicorns were and still are the ruling class possessing apparent immortality. The unicorns were the magi and nobility, based in Canterlot, attending the Royal Magic Academy. The Pegasi were the military cast, Celestia's royal bodyguard, and based in their own city of Cloudsdale to watch over the land from above. And the poor Earth Ponies were the simple commoners and farmers. While the cast system was likely abolished some time ago, there are still traces of it in Equestria today. Look at Ponyville; it was founded by earth ponies, most of them farmers or simple shop keepers. And we learn in Winter Wrap Up that the traditions of ending winter in Ponyville have roots that go back many years to its founding, when apparently magic was not allowed for them to use.
Obviously things are different now, we have earth ponies like Hoity Toity to prove it. But not everything can change overnight. Tying this in with Pinkie Pie, she was born to a lowly family of rock farmers. She had no unicorn heritage, so she could never have been sent to Celestia's magical academy. She indeed had never even been to Canterlot, prior to the Gala. Neither could she fly so she couldn't go to Cloudsdale or hang out with the privileged Pegasi. She had to do everything on her own, the hard way. She wanted to learn, but couldn't go to the Academy, so she took to the library and read everything. She wanted to fly, but wasn't a pegasus, so she built a hot air balloon. She demonstrated overcoming the difficulties in a post-cast society by putting her mind to work and accomplishing everything she set as her goals in life. It is really inspirational when you think of it that way.