In the analysis, a not-so-surprising 52 percent of workers earning between $10,000 and $25,000 annually choose not to participate in 401(k) plans. More surprising is that nearly one out of 10 workers earning more than $100,000 annually also does not participate.

Overall, about 70 percent of workers participate in 401(k) plans, a percentage that has held relatively steady for several years.

Watson Wyatt's analysis is based on about 300,000 workers at 32 large employers that offer a 401(k) and, in some cases, a defined benefit plan.

"Despite employers' ongoing efforts to educate workers on the need to save for retirement, the bottom line is that voluntary participation in these types of plans doesn't work well for everyone, even high earners," said Mark Warshawsky, director of retirement research at Watson Wyatt. "It's one thing to know how much to save for retirement; it is quite another to do it."

Warshawsky notes, however, that participation in 401(k)s could increase in the future as employers are encouraged by the Pension Protection Act (PPA) to automatically enroll employees. Some employers are already taking such steps, and have found that with automatic enrollment, more than 90 percent of employees participate in the 401(k) plan.

While many employers had hesitated to take this approach before because of concerns about, among other things, their fiduciary responsibility for investment results, the PPA may ease this concern, Warshawsky said.

Watson Wyatt also found that employee participation in 401(k) plans does not guarantee a robust retirement fund. Even for those who participate, contribution rates tend to be low, especially among younger and lower-earning workers.

Workers earning between $10,000 and $25,000 annually contribute just 6.2 percent of their salary to 401(k) plans, while workers earning at least $100,000 annually contribute almost 10 percent of their salary. Some high-wage earners, however, may be restricted in how much they can contribute because of non-discrimination rules and allowable legal limits.

The analysis also found that many workers who have been with their current employer for at least 20 years haven't accumulated large account balances in their 401(k) plans. Two out of three workers who earn $10,000 to $25,000 annually and who have been with the same employer for 20 years have accumulated less than one year's annual pay in their accounts. Even in the $75,000 and higher pay category, about one out of four workers comes up short of a year's pay.