Even if it were true that dog's only "love" us for the food and shelter and toys, couldn't we just as easily say that about very small children? Neither can talk, or have an adult's grasp of abstract concepts. Is it possible that, at lower levels of cognition, "I love you because you give me things" is not really different from, "I love you"?
Also, how much of canine affection is like the kind of love one human has for another specific human, and how much of it is loyalty to the group?