People... you can't just take one random percentage and use it for another movie, Twilight had much more room to grow, its opening was relatively modest (compared to uber blockbusters). Plus the math is wrong, the opening increased over 100% from 1 to 2.
Pretty much. Potter and Twilight laid the groundwork. To say it had "just" the book fanbase is seriously underrating the effect the books had. Without the books this would not have been nearly the monster it is now.