Having said that I think there was a bit of "old is bad, our new is good" going on in the late '80s and early '90s. I don't think it was hostile or part of some over all plot to make everyone forget what came before...
actual quotes:
Byrne claims that his depiction of Clark Kent is inspired by George Reeves' Clark Kent on the 1950s television series. "I loved the way he played Clark Kent," Byrne says, "He was grittier, tougher. He wasn't the mild-mannered reporter. He had some guts to him, and that's the way I'm trying to play Clark.
"There won't be as much difference" between the personalities of Superman and Clark anymore. "Clark's not as timid anymore." In the fourth issue of Man of Steel Clark and Lois run into terrorists, "and Clark immediately steps in front of Lois, saying, 'Look out, Lois!'"
"I'm throwing in a little twist of the knife in every issue," John Byrne says, "so if you think you know" the Superman mythos, "there's going to be something in there to let you know that you don't." The first slap to hit readers is the new look that John Byrne has given Superman's native world of Krypton. The next is the new visualizations of Superman's parents, Jor-El and Lara.
"I liked the cold, antiseptic Krypton that I saw in the movie, but we couldn't do it for copyright reasons." - John Byrne
Andrew Helfer reveals that the baby who becomes Superman "is hatched, essentially. You get the impression there's no sex on this world. If you can judge the sexual mores of a society by how high their collars get, on Krypton they go around their heads so just their eyes and mouths are exposed. They're really uptight people."
"When I showed the first issue to Richard and Wendy Pini, Wendy said I'd created a Krypton that deserved to blow up," recalls Byrne. "And that was my intent. I don't want nostalgia for that place. It's very clear in that first issue that Superman is lucky to have come here." Eventually, when Superman learns he is from Krypton, he will declare, "'I'm a human being,' because he doesn't want to be Kryptonian. Krypton is anathema to him."
In the previous Superman continuities, Superman and Batman were the best of friends. In the new continuity, as in Frank Miller's Dark Knight series, the relationship between DC's two greatest superheros is now very different.
In fact, Byrne talked to Miller about the Batman so that in The Man of Steel "I could suggest the kind of Batman he was going to do." Similarly, Miller talked to Byrne so that the Superman in Dark Knight could be based on his version.