Employers' Obligations under 401(k) Plans under Examination

What are employers' responsibilities under 401(k) plans to assure that the fees charged to employees are reasonable?  Class action lawsuits against a number of big companies, alleging that the companies violated their fiduciary duties by not adequately informing employees about the fees and not taking measures to assure fair fees, are exploring that issue.  Courts generally are not granting defendants' motions to dismiss.  CFO.com, Fees Under Fire.