Added the full list :)
As a non-American I'm surprised by the lack of Steinbeck. To me his novels are characterised by his stark interpretations of American ideologies.
Now that you mention it, it's very surprising that there is no Steinbeck. You can't get much more American than the Grapes of Wrath, or any Steinbeck, really. I could have done with fewer mentions of the Catcher in the Rye, but I understand why it's there. I was also glad to see P.K. Dick on the full list.