Norman Rockwell’s Saying Grace became the most expensive American painting ever sold at auction last week, fetching $46m (£28m) at Sotheby’s in New York. ... While most people are still reeling from the financial crisis, the world’s wealth has risen to those at the top. A recent report found there were 2,170 billionaires worldwide, three times as many than five years ago. To many of them, art seems a safer place to spend their money than the financial system – and contemporary art is what comes to market most frequently.