This is a combination of two reports.
From the linked Forbes story:
Though the study’s findings may seem counterintuitive—we think of leaders as pressurized workaholics, especially in these tight economic times—they are consistent with earlier research suggesting that people who have more of a sense of control, are less stressed.
The second, from the American Psychological Assn., Work, Stress, and Health & Socioeconomic Status, cites numerous studies showing that workers on the low end of the socioeconomic ladder are the most stressed, having little to no control over workplace conditions and increased pressures in meeting family and financial challenges.
The people on top not only have more control over their own lives, they have the power to set the terms and conditions for everyone else. Just keep that in mind the next time you hear some rich guy complaining about unions or an increase in the minimum wage.