I still think the statue thing was merely symbolic in the sense that it was one vague hint of Oz's identity. A "real" parent destroying a memory of his son's adoptive ones. As opposed to it being some sort of symbolism that they shouldn't be dead or something.
Superman has enough gifts. I don't want the man miserable by any stretch of the imagination but where is the pathos if he has absolutely everything he could possible ask for? He has a wife and even a son now, he doesn't need the gift of a dead parent brought back to life. Its too much, man. If one gets a hankering for Superman to see his mother again, there's always time travel. There's always flashbacks. There's always dreams.