What is the purpose of a D?

The New York Times published an article titled, "Little as They Try, Students Can't Get a D Here" (August 7, 2010) which described a recent no D grading policy adopted by school board of Mount Olive Public School District in New Jersey. This new policy is an attempt to combat against the practice of grade inflation to raise standards and motivate students to work harder.

The school district is developing a system to help struggling students achieve by providing additional time, three days, to make-up the assignment for a C. Additionally, the school will communicate with parents when students struggle and can provide interventions such as extra-help classes, peer tutoring and evening classes. One must wonder, does this mean that C is the new D?

Source http://www.nytimes.com/2010/08/08/education/08grades.html?_r=1&ref=education