Ok, but even in #663, Morrison repeated the SAME thing you're talking about: The Joker/Batman relationship (loathing/commonality, etc.) and the Joker/Harley Quinn relationship -- basically Joker wanting to be above humanity, but the fact that he cares about Quinn ties him to being human and so he has to kill her.
By now, HQ is important to Joker whether some people like it or not. She represents a facet of his humanity that he just can't get rid of (no matter how hard he tries).
Problem is the Joker CAN'T be this "immortal" being (even tho, yes, he's "died" and come back a gazillion times) b/c this is Batman's world he's living in. And Batman has no super powers -- he's just a man at the end of the day -- so neither should the Joker. What the Joker does have is his insanity.