Nevertheless, the recent tilt towards heavier equity holdings raises questions about whether workers are entrusting professional money managers who might end up buying equities at or near market highs – the S&P is up 189 percent since March 2009.
"Our concern is that this is happening after a pretty good run in the equity market," said Lori Lucas, defined contribution practice leader at Callan Associates, a San Francisco-based consultant to institutional investors. "If it's a reaction to the fact that some target date funds haven't been competitive then it is a concern."
A more aggressive approach has worked for some funds in recent years.
The target date fund families of BlackRock, Fidelity and Pimco have performed among the bottom half of their peers over the last three and five year periods, according to Morningstar. Meanwhile, more aggressive target date fund families, like those managed by The Vanguard Group, T. Rowe Price and Capital Research & Management, ranked among the top half of their peers.
Read MoreA 401(k) fund most retirement savers still can't have
As of June 30, BlackRock's three-year return for its 2050 fund was 10.6 percent, according to Morningstar, compared with 10.16 percent for Fidelity's similar fund and 7.14 percent for Pimco's comparable fund. Meanwhile Capital Research's 2050 fund returned 13.27 percent and Vanguard's fund returned 12.26 percent for the same period.
Furthermore, with average expenses of 0.85 percent per year, these funds charge more than the 0.7 percent in fees levied by the typical actively managed balanced fund, according to Morningstar. The firms' pitch is that investors are paying more for peace of mind and a set-it-and-forget it approach to managing their retirement money. Workers willing to make their own mix of indexed stock and bond funds could pay considerably less. The average expense ratio for an equity index fund is 0.13 percent and 0.12 percent for a bond index fund.
"There is some kind of expectation that we are making these changes because of the equity markets or because of what competitors are doing and that is incorrect," said Chip Castille, head of BlackRock's U.S. retirement group.
BlackRock decided to make its changes after a four-year research project cast new light on how younger workers look at their plans. Previously, BlackRock's funds were focused on making sure that investors had enough at retirement. But given that employees' wages tend to be flat or go up in value slowly, like a bond, BlackRock wanted to make sure that the target date funds were designed to provide greater returns during the course of employees' lifetimes, Castille said.
That, along with the firm's positive 10-year forecast for equities, resulted in the changes, he said.