I'm not sure how the other diets work, but they do work for some people. I once lost 30 lbs with the low fat "Susan Powter craze" (remember that crazy lady with the shaved head?) eating TONS of snackwells cookies (all of them low fat or fat free, of course!)
But I was walking an hour a day, so I think it was the exercise that did it and not what I ate.
I know lots of people that have lost a lot of weight on Weight Watchers and L.A. Weight Loss Centers (on this last one it is really expensive and they don't want to tell you any information on what they eat!)
From all the plans that I have read and know about, I think the LC is the easiest to follow and keep doing in the long run.