There is a difference between a bestseller and a blockbuster.
Bridget Jones Diary The Thorn Birds
Small Island Gone with the Wind
Any mainstream thriller Da Vinci Code
All these books are best-sellers but the ones listed under blockbuster have that common extra factor which boosts them from being a great book to being a blockbuster which you might find on the shelves of those people who do not consider themselves to be book lovers.
Albert Zuckerman in his book “Writing the Blockbuster Novel” identifies as a problem that many authors write commercial books that are “too small”. By too small he means, domestic or limited in the scope of its characters or setting.