quite found his place in the land of the free. As Amir put it,

For me, America was a place to bury my memories.
For Baba, a place to mourn his.

America offered everything that Baba would like to have had in Afghanistan, but it was not like home. The smog hurt his eyes, he got headaches from the noise of traffic, and he coughed from the pollen.

The fruit was never sweet enough, the water never clean enough, and where were all the trees and open fields?

Baba was homesick for his native land and angry about the downward spiral that his life had taken. Once a powerful man, he was reduced to pumping gas in California. Perhaps the final straw for him came when the manager of a local market that Baba had patronized for two years asked for his ID in order to write a check. In Afghanistan, a man produced a stick to obtain credit. A notch was made in the stick to denote the amount owed. Trust was different in America, and life was different than in Kabul. Baba's English was poor and he was not respected as he was in his home. He saw the greatness in America, but he also saw that it was going to pass him by. 

This quote expresses the truth that Baba loves the idea of America but "living" in America gives Baba an ulcer.  Hosseini includes this quote not only to portray the difficulty that many immigrants encounter as they try to adjust and be successful in America but also to give the reader a slightly autobiographical glimpse into his own family's early life in America.

Baba and Amir choose America to flee to because Baba sees it not only as the land of opportunity, but also because he admires America's rough, adventurous reputation.  While in Afghanistan, Baba emulated America's Wild West with his car, bold attitude, and swagger.  When he arrives in America, however, he finds that his sway in Afghanistan has disappeared.  His name means nothing in his new country.  Once known by all in Afghanistan, in America, Baba is forced to work long hours for a pittance and show identification in order to make minor purchases.  He is out of his comfort zone and must worry about how he and his son will survive.  Like many immigrants, Baba grew up with a glorified view of America but finds it difficult to make his dreams come true in actual America.

In regards to a second reason for including the quote, I believe that Hosseini wanted to pay homage to his own father in a sense.  Like Amir, he fled his homeland with his father and family when Afghanistan was no longer safe.  His father was a diplomat for Afghanistan and well respected.  When they moved to America, he was forced to take whatever job he could and worked long hours for minimum wage to provide for his family.  Hosseini himself loves the idea of America but stresses here that success does not come to Americans without hard work and some pain (i.e., the ulcer).