That is not entirely true, as the character is Aeris in the PAL version as well. ^^
As such, it is how I was introduced to the name, and is how the name will forever remain to me. On top of that, in my native tongue, Finnish, the name is pronounced very similar to the way it is in Japanese.
The languages have many other similarities other than that, or so I seem to think.
Both transliterations have basis; I know the stories and agree, but I simply can't think of Aeris as Aerith even if it officially is written like that in non-Japanese.The JP materiels spell it in Roman letters with a TH, and all English content afterwards has been consistent with that spelling. The early PS1 games were translated by the JP department, not localized by an American branch. There were tons of spelling and grammar errors in those releases.
It was/is more personal preference than anything else, and that's why I wrote I would not use the name as an example. I never intended to try to argue which is correct and which is not, for to me, there can be only one. :]
Thinking back to my comment about faith, I probably had fate (feito) in my mind for some reason and that's why I first felt feisu would not fit with faith.