Well, in the case of Gerard Christopher (The Superboy series), it makes sense that he would emulate Chris Reeve since that show was produced by the Salkinds, who, as I'm sure you know, produced the Reeve films. So the simularity in that case was no doubt intentional. And in the case of Dean Cain, you probably think he makes a stronger Clark Kent because you're SUPPOSED to. The whole point of the characterization in that show was that Clark Kent was the real person, while Superman is the disguise that lets him use his powers in public. In fact, one of my favorite second season episodes addresses this when Clark tells Lois, "Superman is what I can do, Clark is who I am.".