It's just numbers. A lot of the people posting here probably grew up with Lois & Clark as their first or primary introduction to Superman, whereas The Adventures of Superman is harder to come by these days. So even though Cain bears probably less resemblance to the Superman of the comics than any other listed actor save Routh, they see him as "their" Superman.
My primary introduction to Superman was the Superfriends cartoons, and I've seen every Superman on that list except for Kirk Alyn and contrary to the general consensus around these parts I think Dean Cain makes a great Superman because I'm not just looking at his face
. Cain is the only one that actually looks like he's built like Superman. Routh is a stick. Welling is an emo athlete. The only thing that Chris Reeve has going for him is his haridresser was smart enough to put a spitcurl in his hair. And, I'm sorry all you George Reeves lovers...he wore padding!