America’s superrich just keep getting richer.Forbes on Monday released its annual list of the top 400 richest Americans. While most of the top names and rankings didn’t change from a year ago, the majority of members of the elite club saw their fortunes grow over the past year, helped by strong stock and real estate markets. Microsoft Corp. co-founder Bill Gates remains America’s richest man, taking the top spot on the list for the 20th straight year, with a net worth of $72 billion. Investor Warren Buffett, the head of Berkshire Hathaway Inc., keeps second place with $58.5 billion, while Oracle Corp. co-founder Larry Ellison stayed third with $41 billion. Brothers Charles and David Koch, co-owners of Koch Industries Inc., stay tied for fourth with $36 billion each. Wal-Mart heirs Christy Walton, Jim Walton, Alice Walton and S. Robson Walton took the next three spots, with holdings ranging from $33.3 billion to 35.4 billion. New York City Mayor Michael Bloomberg, the founder of the eponymous financial information company, rounds out the top 10 with $31 billion. According to Forbes, the 400 people on the annual list posted a combined net worth of $2 trillion, up from $1.7 trillion a year ago. That marks their highest combined value ever. Meanwhile, the average net worth of the list’s members rose to $5 billion, the highest ever, up from $4.2 billion in 2012. Net worth grew for 314 members and fell for 30 members, Forbes said. Net worth for America’s wealthiest people have risen in the years since the financial crisis, widening the gap between the exceptionally well-to-do and the rest of the country. According to a study of Internal Revenue Service figures released last week, the top 1 percent of U.S. earners collected 19.3 percent of household income in 2012, their largest share in IRS figures going back a century.