LOL - I don't think it has anything to do with that.

I believe the difference comes from the fact that there are 2 translations of FF5 from Japanese to English. The first one was a fan-made ROM translation created closer to the time the game was originally released in Japan (mid-1990s). This translation used names like Batz, Lenna, Cara, and Ex-Death for its main characters, and is generally considered the "better" translation.

The second is the "official" translation, made by Square when it finally released FF5 outside of Japan as part of FF Anthology for the PS in 1999. This one used names like Bartz, Renia, Krile, and X-Death. This is generally considered the "crappy" translation.

Since most FF fans prefer the old fan-made ROM translation, they still refer to characters as Lenna or Ex-Death as opposed to the actual Square names. So really, its all a matter of opinion; personally, I prefer Ex-Death because X-Death sounds really cheesy.