My big dog sometimes leaves some of his bones or meat for the small poodle. He eats then steps backwards and allows the little one to eat. He also shares he's dog food and sometimes they even eat out of the same bowl. He's always been like that though when we got him he wouldn't mind you taking the food out of he's mouth even, he would let you, i dont know if its just the way he was raised. He doesnt feel intimidated or worried around food its like he knows there'll be more so he doesnt have to worry about it.
The poodle on the other hand will NEVER share, he growls and runs away with his food... greedy little bastard.
So i think its more about conditioning than a moral code.