I'm not really a snob....
No serious dog person I know of feeds crap food like Pedigree or Iams...
...that a: I would quickly hear from someone who did, and b: I'm sure I know plenty of "dog people" who feed kibble and I shouldn't be so snobby about it!
In fact, the oldest dog I knew personally was a little yellow mutt named Chester who ate the weird red colored Alpo kibble and lived to be just about 23 years old.
So genetics and luck probably trump diet any day.
And feeding dogs is (or certainly should be) a fairly minor part of our relationship with them. If I were rehoming a dog I'd go for a home that fed whatever if the dog was trained and worked and a part of the family, any day, over one fed a carefully crafted diet but didn't get out much or got stuck in the back yard understimulated much of the time.
Still, my dogs would probably be sorta bummed if I stopped giving them things like lamb necks, deer carcasses and whole chickens and started giving them nothing but pellets!