Just like Mass Effect! (I wonder if that was an intentional copy on Square's part) "Faster, and more western-style combat" is the current goal of many JRPG companies AFAIK, due to the relative sales of recent JRPG vs western ones.
The actress is Australian, so she actually does, not merely "supposed to". The "weirdness" apparently comes from that she was instructed to try to sound "not so Australian" (and younger)----and what you get, is Vanille. This is what her normal voice/accent is: http://www.youtube.com/user/GeorgiaVC#p/u/6/JVc1JXTQDf8
(somewhat ironically, Fang's actress is American)