Take Bill Gates - I don't know his net worth off hand, but it is upwards of $60 billion. I think he owns around 15% of Microsoft's stock. Do you think that he could extract all of his wealth if he wanted to? What do you think his true wealth would be in actual dollars? What would Microsoft's stock do if Bill Gate's sold half of his shares, just due to the new available supply? What would Microsoft's stock do if Bill Gate's sold half os his shares, just due to investor's reactions of the primary shareholder liquidating? My point is that the wealth numbers you see are paper wealth. What's important is the actual wealth than can be used to purchase and consume products and services.
Many if not most of the richest individuals are in a similar situation. That being said, so what even if the income inequality is true to the extent you report? The wealth of the richest has been earned, if not by them, by their parents or grandparents. Their wealth is being used for research and development, paying employees, as monetary capital in the businessworld. It is also arguably the most efficient use of capital, because it is being controlled by those who are most successful.
More than anything, the ability to amass wealth provides the greatest incentive to be productive. This incentive impacts all of us from the poorest to the richest and is what has provided the environment that has allowed the US to be the greatest economic force in the world.