User blog comment:ClariS/Why Xerath's Passive is Bad/@comment-163.191.194.60-20130320135709/@comment-163.191.194.60-20130322194017

Because Nocturne has been pulled into the physical world (out from the dream world), by being bound to a nexus fragment, and thus is an entity entire physical? That would be my first guess, but I would assume that since Xerath already had a large armor buff passive, that Riot didn't want to make another one at that point in time. So intead they made his passive heal him on-hit, similar to how he vamp'd off of people's nightmares.

Zac on the other hand has a pssive that fits his lore-them exaclty, so don't know why you'd bring him up.

Either way, it's clear enough that the Lore supports Xerath's passive plenty and I don't see how someone can say that it doesn't.