Ok, so Ah posted something on the Quintessence art fanworks thing, and it seemed to be getting some positive feedback. Please don't lynch me for this, but it gave me the courage to post fan works of To The Moon on this as well...
If any part of the story in To The Moon should actually be captioned with the title "For River," Ah think it should be when they were kids in junior high school, at Johnny's first confrontation of River by the stairs.
Since you're experiencing the whole tale backward, rooting since after the time Johnny allows River to die in the place of her lighthouse, from as far as Johnny can possibly remember, this moment is where it all started.
This moment is the first one that ever fueled his decision to give up someone he loves for the sake of her happiness. This moment is where River first expresses her own passions and desires to Johnny, so it should be the piece titled, "For River." It was the hardest thing he'd ever had to do, after all. Him letting her go was the time that was entirely made for her... not the song.
If you don't agree, well..... Please don't stab me, Dad. Ah do my best! >.<