Research, in fact, shows that money from a traditional pension - combined with Social Security - generally replaces 56.3 percent of a couple's pre-retirement income, while a 401(k) combined with Social Security substitutes for just under 43 percent. Social Security alone replaces 34.4 percent. Some pension plans - particularly those in the public sector - replace an even greater percentage of salary.

"Having a pension and Social Security [combined with private savings] allows most households to live as well after retirement as they did before," said Alicia Munnell, director of the Boston College Center for Retirement Research, which studied the topic. "If you don't have a pension, you'll have to tighten your belt in retirement."