@ATC: Hearths Warming Eve pretty much comes out and says that only the
E Ps can grow food in sufficient quantities to feed everypony, which is a pretty enormous deal. While I have no doubt that a pegasi or unicorn could grow a garden or something, I doubt they'd be able to produce that much. The other thing is that it's
really strongly implied that the average EP is much more physically resilient than the average unicorn or pegasi. RD and Twilight aren't really good barometers given that both of them are near the pinnacle of their respective races. Twilight in particular is pretty much the strongest unicorn we've seen, so the fact that
she has really good telekinesis doesn't imply that all unicorns could do anything close to that. The other thing is that as noted, we've only seen her do the apple thing
once, and there's no indication that she'd be able to keep that up for any length of time. Not to mention that whenever we see something requiring large amounts of physical strength (pulling a train, construction work, etc.) nine times out of ten it's Earth Ponies doing the work, which implies that on the whole they're stronger.
The other other thing is that simply being able to harvest those apples faster doesn't mean she's better at planting, caring for, selling, or otherwise utilizing those apples. Even if we accept that Twi could harvest faster than AJ, I think it's pretty obvious that if you gave each AJ and Twilight a farm to run for a year, AJ would probably grow way more product, and of much higher quality.
TL;DR the Earth ponies are the
Boring, but Practical race; they don't have the flashiness that unicorns or pegasi do, but without them Equestria would collapse pretty quickly.
edited 31st Aug '12 11:52:54 AM by JapaneseTeeth