In an essay in this newspaper last fall, Peter Cappelli, a professor of management and human resources at the University of Pennsylvania's Wharton School, challenged the oft-heard complaint from employers that they can't find good workers with the right skills. "The real culprits are the employers themselves," he asserted.

"It is part of a long-term trend," he adds in an interview, "and the recession caused employers to be able to be pickier, to get even more specific in the...