The authors of the EPI report, Jared Bernstein and Larry Mishel, point out that although college graduates are better off financially than other groups, they no longer are insulated from the problems plaguing the workforce at large.

With globalization threatening white-collar jobs, college-educated workers are more vulnerable than before to being unemployed, the analysis shows. And while college-educated workers top the earnings scale, the rewards of the economic boom are not shared equally among college grads.

To find out why there is such a wage gap, Bernstein and Mishel say you need only look how wages have stagnated over the past six years. While the pace of productivity growth has accelerated, wage growth has not kept pace. Between 1980 and 2005, productivity in the U.S. economy rose 71 percent, while the real compensation (including benefits!) of nonsupervisory workers rose only 4 percent. And nonsupervisory workers make up about 80 percent of the workers.

Another factor behind stagnant wages and growing inequality is the steep drop in unionization rates (from 25 percent in the late 1970s to less than 12 percent today).

The Employee Free Choice Act, introduced this week, would go a long way towards making the process of choosing a union more fair. With more workers in unions, the wage gap would be significantly lower, because union workers make on average 30 percent more than nonunion workers, and 80 percent have health care insurance, compared with about half of nonunion workers.

Also, less-educated workers are more likely to earn the minimum wage, which has not been raised in 10 years. The House and Senate recently passed the first increase in the minimum wage in a decade, raising it from $5.15 an hour to $7.25 over two years, although the two chambers still must agree on the details of a final bill.

Another factor is the growing trade deficit and globalization. The trade deficit, which is expected to reach $230 billion this year, has contributed to the loss of nearly 1 million manufacturing jobs since 2001.

According to the EPI analysis, all these elements demonstrate that education alone cannot explain why the wealth gap is growing:

Policy makers and analysts must avoid reducing the inequality debate to a sole explanation regarding education. For any individual making a decision about their future, and for any society contemplating useful investments, education is an obvious and important area to consider. But it is not solely responsible for the growth of inequality, not over the longer term, and especially not in recent years.

Thus, other policies—minimum wages, a level playing field for union organizing, health care and pension provision, work supports for low-income workers, full employment, and responding to the downsides of globalization—also need to be pursued.