Investing can be as simple as buying great stocks when they're on sale, even if you're a billionaire.Wall Street works for everyone, but some of the ultra-wealthy billionaires seem to have a certain aura about them, as if they have some inside track on the market's pulse. These folks tend to manage money for clients or themselves and, because the amount they manage is so large, they are required to maintain some transparency by filing quarterly 13F filings to reveal their recent trades. These filings give i ...