Update: Nintendo confirmed the delay, stating:
The launch date for Metroid: Other M has shifted to Aug. 31. As you may know, this game is the product of a unique partnership between longtime Metroid producer Yoshio Sakamoto, Team Ninja and many other individuals and groups, all of whom have set very high standards for this latest installment in the series. Although it's taking slightly longer than expected to complete the project, we're confident that fans will find it to be well worth the wait.
Video game development is a lengthy and complex process. We have always put the quality of our products first, and have historically taken the time needed to make our games meet the expectations of our fans.