1/10 Subway Stalinist
I think I understand that. IMO, the "ego" piece is implied by the idea of reward and punishment.I see one big difference between the two, that you may not have noticed. In heaven/hell, it's the individual person that is rewarded or punished. In reincarnation, that individual person of a single lifetime is dead, gone, kaput, as it is the soul that moves on. So yes, in heaven/hell view there is attachment to the ego, but not to in reincarnation. Of course there are some people who think it's the person that reincarnates, but that's not the traditional understanding. Those folks often think they will be the same gender, have the same interests, etc.
If your next life that's being rewarded or punished isn't "you," then how could it be a reward or punishment?