A velvet glove conceals the iron fist.

It may be that successful mean people just hide it well enough to seem nice and the "x-ray vision" of the author's wife doesn't work on everyone. Once a mean person's position is unassailable, the velvet gloves come off. Alternatively, money is power and power corrupts.

The current crop of billionaires are at the pinnacle of success (depending on how you define it), but most sure don't seem very nice, and that's with a large PR team working overtime to hide the meanness.