Christopher Reeve did such an amazing job that to give him some kind of accent or more bravado would have been wrong. Audiences wouldn't have responded to that either.
I could finally quit my job as a bartender and stop dreaming that I might be Superman and know that I was. Then I started thinking about how cool it was.
Chris did such an amazing job. You can change things, but if you do it could be horrible. When somebody does something so great, there's certain things you can tweak, but to change it just to change it sometimes is dangerous.