He might very well be the only actor in Hollywood that can be considered "bankable." Especially now since his sci-fi/horror flick I Am Legend has broken the record for a December film opening.
Now many are wondering why his movies are usually profitable when so many others on Hollywood's 'A-List' couldn't fill a theater if it was the only place on Earth safe from a rampaging horde of poo-flinging, blood drinking, brain-eating vampire-zombie monkeys.
I can answer that.
The audience trusts him and Will Smith trusts the audience.
Will Smith knows that his fortunes ride on the good-will of the American public, not on the whims of fashion as dictated by Hollywood's select few, or the by who the paparazzi stalk the most.
He lives outside the epicenter of the Hollywood frenzy, and only appears for the paparazzi at premieres, charity events, and award shows. You don't see him in the tabloids, cocaine caked on his nose, being dragged out of his mansion by police. In fact, he makes a point to have a personal life that, despite his wealth, is as boringly normal as everyone else.
This aura of normalcy, combined with his easygoing charm, and his talent as an actor, allow him to connect with the audience on an emotional level.
Plus there's also his careful selection of projects.
Most 'A-List' stars base their decisions on ego, money, and acceptance by their Hollywood neighbours. But what your ego, banker, and your Hollywood-type neighbours want to see are not what the average American wants to see.
Will Smith's choices are based on what he thinks the audience wants to see, primarily what he would pay money to see if he was an average middle class American.
They want a good guy who fights bad guys, action (it is called the Motion Picture for a reason) thrills, chills, and some humour. They don't want to see boring, repetitive tales of suburban angst that have more to do with life in Beverly Hills than the average suburb. They don't want to see films where they are insulted through 1 dimensional caricature for being religious, patriotic, or not being as fashionable as the folks in Malibu.
Plus they know that Will Smith works hard at his job. He doesn't blow off work to go party and drive drunk. He's an entertainer and he knows that it is his job to entertain the general public, and that it is a job that he has to do to the best of his ability in order to stay on top of the food chain.
The audience knows that on an emotional level, and they respect it.
And that's why he's one of the last movie stars in Hollywood. "What did you say Lassie? Hollywood's profits have fallen down a well?"