Actually I was under the impression that it can become th or su, which is why I said equally correct, even though that would actually make it become Aerisu, which sounds silliest of all, but it's not a stretch to imagine the u just being dropped. My mention of the lack of a th sound in the Japanese language was pretty meaningless though I don't know why I brought that up. In any case, I'm more inclined now to think it was a simple mistake based on titeguy's observation, and even though it sounds nothing like earth really, I certainly don't find it too annoying that I couldn't rapidly get used to Aerith.
And if Opine is correct, then I definitely consider that a phonetic improvement, at least in the bland western accents that I imagine most or all of the VA will be in.