The rule for figuring out whether the pronoun after "than" is "I" or "me" is what it's doing in the sentence. This applies to all pronouns as well.
I like The Beatles more than he.
I like The Beatles more than him.
The second one sounds right, but in the context of the sentence the first one is actually correct. To make what the two sentences are actually saying more clear:
I like The Beatles more than he (likes The Beatles).
I like the Beatles more than (I like) him.
With that in mind, the second one now looks silly, since you're comparing the value of you and your friend's opinion of The Beatles, not whether you prefer The Beatles to your friend.
The same applies for I and Me:
He is taller than I.
He is taller than me.
Again, the latter sounds correct, but in actuality it's the former:
He is taller than I (am).
He is taller than (he is) me.
However, it's worth noting that if college students and even professionals can make this error, the main characters in an average JRPG--i.e. usually a bunch of high-school aged students who probably aren't known for their academics, except of course for the token brainy one--probably aren't going to know any better.
On another topic, is anyone working on making a graphic hack to give us the battle sprites from the PSP version? After having seen the screens these guys look so chubby by comparison.