Beware of surveys. Even though I posted the survey results. That survey was done in 1991, and did not contain a wide cross section of respondents... it was targeted to the Book of the Month Club, and Library of Congress users... not the typical American. Also it asked for the most influential book, not a ranking of books by those surveyed.
Most Americans would probably say the Bible is the most influential book... it has the most impact on our society... even if you have never read it. Also, how many people have read the entire Bible?
What influences people to read a book? Often the NY Times Best Seller List, Oprah's recommendations, and required reading in school. Many schools have gravitated away from the "classics" and there are more current novels read, "because the classics are not relevant today" -- this statement of fact, was thrown at me by one of my children's teachers when I was frustrated with the curriculum that was influencing my kids, which required my intervention and supplemental reading at home to ensure they received a quality education.
Atlas Shrugged is influential, if you just look at the number of copies that have been sold every year since 1957.
Here is another list.
25 BOOKS THAT HAVE SHAPED READERS' LIVES
Library of Congress, Center for the Book
1. The Adventures of Huckleberry Finn, by Mark Twain
2. Atlas Shrugged, by Ayn Rand
3. The Autobiography of Benjamin Franklin
4. The Autobiography of Malcolm X
5. The Bible
6. The Catcher in the Rye, by J.D. Salinger
7. Charlotte's Web, by E.B. White
8. The Diary of a Young Girl, by Anne Frank
9. Don Quixote, by Miguel de Cervantes
10. Gone With the Wind, by Margaret Mitchell
11. Hiroshima, by John Hersey
12. How to Win Friends and Influence People, by Dale Carnegie
13. I Know Why the Caged Bird Sings, by Maya Angelou
14. Invisible Man, by Ralph Ellison
15. The Little Prince, by Antoine de Saint Exupery
16. Little Women, by Louisa May Alcott
17. The Lord of the Rings, by J.R.R. Tolkien
18. Roots, by Alex Haley
19. The Secret Garden, by Frances Hodgson Burnett
20. To Kill a Mockingbird, by Harper Lee
21. Treasure Island, by Robert Louis Stevenson
22. Walden, by Henry David Thoreau
23. War and Peace, by Leo Tolstoy
24. What Color is Your Parachute?, by Richard Nelson Bolles
25. The Wizard of Oz, by L. Frank Baum
P.S. The Fountainhead and Atlas Shrugged were not on my required reading list for my kids, although both were given copies as gifts when they were older. I don't know if they read them. Once they completed high school, as adults the content of their continuing education was up to them. I provided 1/2 of the cost of college if they wanted to continue, did not guide or influence them in their course of study, and fortunately both did graduate.