The estimated delivery date is intended to set expectations for backers on when they will receive rewards. Setbacks are possible with any project — creative ones especially. When the unforeseen occurs, creators are expected to post a project update explaining the situation. Sharing the story, speed bumps and all, is part of the Kickstarter experience.
Creators who are honest and transparent will find backers to be far more forgiving. We’ve all felt the urge to avoid things when we feel bad about them, but leaving backers in the dark makes them assume the worst. It not only reflects badly on the project, it’s disrespectful to the support that community has given and to other Kickstarter creators. Regular communication is a must.