NEW YORK — For the first time, Forbes magazine’s list of the 400 richest Americans consists exclusively of people worth $1 billion or more. As a group, the people who made the rankings released Thursday are worth a record $1.25 trillion, compared with $1.13 trillion last year. In the billionaire-athon, casino magnate Sheldon Adelson pole-vaulted to No. 3 from 15 in last year’s ranking, finishing behind the mainstays at Nos. 1 and 2: Microsoft Corp. (MSFT) (MSFT) founder Bill Gates and Warren Buffett of Berkshire Hathaway Inc. (BRKA) Adelson is now estimated to have $20.5 billion, Buffett $46 billion and Gates $53 billion. Gates has held the No. 1 spot for the last 13 years while Buffett has been No. 2 every year since 1994 except 2000, when Larry Ellison of Oracle Corp. (ORCL) held that spot. Adelson’s expanding net worth is related in no small part to his decision to open a casino two years ago on the island of Macau, an emerging gambling haven off the southeastern coast of China. Profits are growing rapidly thanks to the Las Vegas Sands Corp. (LVS) (LVS)’s Macau casino. Adelson personally and through family trusts controls 70 percent of […]