You wound me. Of course I know about Lauren Faust's account.



As for why their currency is named with a horse pun (and may be gold-standard-based, some-other-standard-based, or a fiat currency), you might as well ask why most of the cities and many of the citizens of Equestria are named with horse puns. Extradiegetically it's quite self-explanatory; intradiegetically it admits no end of supposition but no beginning of any support for any particular explanation. (Although a better question is why so many things in the Equestria Girls universe are also named with horse puns.) Personally, I favor the intradiegetic explanation that everything is being translated from Ponish to English for our benefit and the translators just like puns (and that when Twilight goes through the mirror, the magic of the mirror translates everything from English to Ponish for her benefit, so by convention everything in the Equestria Girls universe is automatically translated from English to Ponish before being translated back to English).