In a world where Twilight Sparkle, an out of shape book worm, takes a number of lethally heavy objects to the head with no damage. And Derpy takes a lightning bolt and is barely singed.
Who says Twilight is out of shape just because she's a bookworm? The girl placed 5th in a footrace despite not training for it or considering herself an especially skilled runner.
Come to think of it have we EVER seen Twilight exhausted from physical exertion?
Proof-reading is totally unnecessary in the digital age now that we have spell cheque.