According to Forbes, Bill Gates of Microsoft (NASDAQ: MSFT) is no longer the richest man in the U.S. The honor now belongs to Warren Buffett, the head of conglomerate Berkshire Hathaway (NYSE: BRK.A). Buffett is worth $62 billion to Gates's $58 billion.

This says more about the shift in the American business landscape than it does about anything else. The Berkshire Hathaway stock is up 30% over the last year, while Microsoft's is flat. Since Berkshire owns an insurance company, it would make sense that the financial crisis would hurt its value, but Buffett has stayed away from the investments that have hurt other companies.

Microsoft may be a safe investment now with its large cash position and steady income from Windows, but it is probably no longer a growth stock. Microsoft software runs on 95% of the world's PCs and many of its servers. That leaves the question of what the company can do to expand rapidly again. The answer may be that it can't.

Buffett's company is in more than a hundred businesses. He can make the argument that diversification is the foundation of a successful corporation. The firm's operations make everything from uniforms for police to concrete block, roofing systems to fabrics. Berkshire also owns large parts of companies from American Express (NYSE: AXP) to Wells Fargo (NYSE: WFC).

The new Forbes ranking shows that a large bucket of good investments trumps owning a piece of one successful company in a market that is no longer growing quickly.

Douglas A. McIntyre is an editor at 247wallst.com.