Should 401k Plans have only Index Funds?

A nice article about how 401k plans are better off with only index funds.  I do have a quibble with the article.  Index funds generally outperform actively managed funds over the long run due to their lower fees.  Looking at the last 10 years, all of the index funds I have recommended for 401k plans have performed in the top half of their peer group, and most in the top third, due to significantly lower fees.