Depends on the person, someone people just get wealth thrust upon them through no cause of thier own. I.e the landed gentry, people who inherit wealth, models/singers who do very little to earn their money.
But then some businessmen who have built themselves up from scratch are definitely where they are today because they are more intelligent/have more motivation than others. Good examples would be the likes of Richard Branson or the Dragons from Dragon's Den, all of whom are self made multi-millionaires and in the case of Branson billionaire.