I know some people don't have problems with SD. It's something I wouldn't choose to feed. If it was a life or death situation and my dog needed to be on a SD RX food or something, then I would, but it would never be my first choice. I think it's highly over-rated, I don't particularly like the ingredients, and feel that a dog can eat way better.
A person can live 100 years eating junk, smoking cigarettes and drinking beer every day of their lives, does it mean they are necessarily healthy? Just like a person who exercises every day, eats all organic, and doesn't drink or smoke can die of a heart attack at the age of 50. Crap happens and sometimes it just doesn't matter. But just because a dog DID live to be 15 or 16 on Pedigree doesn't necessarily mean they were at their healthiest or there's no way of saying if that dog would have lived to be 20 on a different food. There are just far too many factors involved and you gotta do what you gotta do
I just prefer to feed foods without corn and unnecessary things for a dogs system in large quantities.