See I was content with the ending. The story wasn't about their entire life but about this one driving factor in brad and luke's life. That factor has since been closed and done with. To see that they lived past the times of their fighting and now are within a "normal" society style (as per grandpa luke), the assumptions that we conclude to give a decent range of happiness and mystery as to how they went on afterwords. These type of endings are nice since they give the ending to the reader and allow them to fill in the gaps the way they want it. When a manga...or story for that matter...gives a definitive ending...it can leave a bad taste in peoples mouths.