Something else about the dropout rate; the dieters were randomly assigned to a diet and didn't get to choose which one they would prefer. This doesn't reflect real life where the dieter chooses which program they wish to use and would therefore have a higher liklihood of picking something that suits them and they can commit/stick to.
IIRC, there was also very little education or support offered to the test subjects as well which would also contribute to the contrition rate. They were handed a diet sheet told to read and follow it and sent on their way.