Just to add my two cents. Superman has a certain look so it shouldn't surprise anyone that Reeve, Routh and Cavill all bear a resemblance to one another. They have all been made to look like Superman. In my mind, Reeve did not define what Superman should look like. Reeve simply looked like Superman.
I don't think that G. Reeves looked much like the Superman of the modern era, but he did have the qualities of a 1950's Superman with slicked back hair and a broader, less angular jaw.
While I enjoyed Dean Cain, I think his Clark looked better than his Superman.
To sum up (because I have started to ramble), I think the three big budget franchises and to some extent, Smallville, chose actors who all had the basic features of the Superman character.