I think the reason that the main character in FFs or other RPGs never says "I Love you" is because he/she is supposed to be tough and strong. Also, in the case of a guy, add macho to the list. For a tough person to say "I love you" would tend to make them look weak and vulnerable. And this is not what game companies want.
They figure that games will sell better w/tough unfeeling heros and heroines. This, of course, is just my personal opinion, but from what I have seen, I think it tends to be true.
sincerely,
sx/amiga