Which significance has it had, that Hosseini has written the novel as an expatriate writer (has written the novel in excile in USA - western influences), for the social reality in Afghanistan that the book looks to portray?
The mere fact that the novel is written in English means that the author's experience as an expatriate has already had a profound influence on the book. The author has lived outside of Afghanistan for most of his life, coming to the U. S. at the age of 15 as a political exile from his native land. Interestingly, a book that had a strong influence on him after his arrival in the U. S. (and after he learned English) was John Steinbeck's The Grapes of Wrath. Steinbeck, in that novel, dealt with a nation in turmoil and undergoing great social changes. The potential relevance of Steinbeck's novel to Hosseini's writings about Afghanistan is intriguing.
Here's a very helpful link:
Writing this novel as an expatriate surely influenced the author's attitude about some aspects of life in Afghanistan. The novel portrays the suffering experienced by women. I remember reading a review when the book first came out that criticized Hosseini for not addressing the effects of US occupation on Afghan women. I don't remember details about that, but it seems reasonable to assume that western influence could possibly be why Hosseini didn't include this in his novel.
Hosseini's father was a diplomat who lived much of his life in Paris, so Hosseini grew up experiencing the subtleties of the political situation in Afghanistan. Much like Baba, he was fascinated with the United States and the freedoms it offered. The author obviously disdains the ultra-conservative political situation there in which religious beliefs dictate the law. Hosseini misses his homeland of old, but not the Taliban influences which tore the nation apart.