It’s been a good year for billionaires. But the fortunes for mere multi-millionaires haven’t been as bright.

The number of billionaires in the world grew 9.4 percent to 2,160 people over the past year, according to Wealth-X, the Singapore-based wealth research firm. Billionaires' combined wealth grew by $760 billion, to $6.2 trillion.

At the same time, the number of people worth $30 million or more grew by only 0.6 percent. There are now 187,380 people in the world worth $30 million or more. Their combined fortune fell 1.8 percent to $25.8 trillion. Hardest hit were those worth between $200 million and $500 million. (Read more: Salaries of the Wealthy Still Falling )

Why the diverging fortunes for the super-rich and the merely rich?

Mykolas Rambus, Wealth-X's chief executive officer, said that billionaires get better financial advice. "Billionaires outperformed the markets while the rest of the world's UHNWIs struggled to keep pace. There are clear opportunities for advisers to replicate investment strategies of billionaires for their UHNW clients," he said.

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