Don’t be fooled by CEO exits at Hewlett-Packard, General Motors and Sara Lee this month. Chief executive officer turnover has fallen to a five-year low and may not rise until the economic outlook clears and stock-option values rebound.

There were 709 CEO changes in 2010’s first half among publicly traded companies in the U.S., down from 871 a year earlier and 1,482 in the first six months of 2006, according to New York-based Liberum Research, which tracks those changes.

“Boards were looking at their CEO and saying, ‘You’re not going anywhere. We’re in trouble right now and we need you to stick around and sort this out for us,’” said John Wood, chief of CEO and Board Practice at Chicago-based Heidrick Struggles International Inc.

“C-suite churn” sliding to levels not reached since at least 2005 shows how directors prefer to shake up top management in good times and stick with “the devil they know” during a recession, said Gail Meneley, a co-founder of search firm Shields Meneley Partners in Chicago. C-suite refers to top managers with title acronyms that begin with the letter C, such as CEO, CFO, COO and CIO.

Turnover will probably stay low into 2011 as the strength of the recovery remains in question, she said.

“Boards adjust their expectations based on external factors just like they adjust based upon internal factors,” said Maggie Wilderotter, CEO of Frontier Communications Corp. and a Procter Gamble Co. and Xerox Corp. director. “The economy is a big external factor.”

The departures of Mark Hurd from Hewlett-Packard and Brenda Barnes from Sara Lee were atypical because they weren’t linked to company performance, Wood said.

Hurd, 53, was forced to resign on Aug. 6 after an internal inquiry turned up faulty expense reports and a personal relationship with a contract worker. Sara Lee said Aug. 9 that Barnes, 56, stepped down as chairman and CEO for health reasons after a stroke in May.

Directors’ desire for continuity shaped CEO Ed Whitacre’s decision to step aside as GM plans an initial public offering to cut the government’s 61 percent ownership stake. GM’s board and bankers asked Whitacre, 68, to agree to leave now or stay for years more to ensure the success of the automaker’s IPO, three people with knowledge of the matter said.

The embrace of CEO incumbency stems from the same caution that’s swelling corporate treasuries with record hoards of cash, said Jeffrey Sonnenfeld, associate dean of the Yale School of Management and head of the Chief Executive Leadership Institute. Companies in the Standard Poor’s 500 Index had $1.24 trillion in cash at the end of the most-recent quarter.

“Now we’re seeing excessive risk aversion,” he said. “We’re seeing too much conservatism.”

The silver lining: Boards that once celebrated “swashbuckling” risk takers at the helm now are promoting from within and planning better for succession to cut the disruption from a leadership change in tough times, Sonnenfeld said.

CEO turnover in North America dropped in 2009 to 12.4 percent from 14.8 percent in 2008 and 15.6 percent in 2006, according to the report, which surveyed 2,500 companies worldwide.

Changes linked to mergers and acquisitions slid to 2.1 percent last year, from 4.6 percent in 2006. Forced exits accounted for 1.5 percent of the departures, compared with 4.3 percent in 2006, the Booz researchers found.