This is so true, especially in the case of Baba, and to a lesser degree with Ali and Hassan. Baba has a great deal of trouble expressing his love to Amir, in part because of the blame he places upon his son for the death of Amir's mother during childbirth. His love for his son grows as Amir becomes an adult in California, and he is willing to give more of himself as his illness takes its toll. Baba works long hours at a lowly job to make ends meet for him and his son, and the two of them seem to bond on their flea market weekends. Baba's past lies, however, come to haunt Amir, and cause him to question his father's sincerity and intentions.
Ali keeps the knowledge of the true paternity from Hassan, yet his love for his "son" is unquestioned. He accepts the child as his own and continues his humble position until his own pride forces him to leave Baba's house following the theft accusations against Hassan.