I have not followed one of the diets in the Prevention issues, but I do follow a similar program.
I am a calorie counter, and I eat a calore controlled diet, and try to make as healthy of choices as I possibly can-BUT-I simply cannot follow a weight loss/maintenance plan where certain things are actually "forbidden". Even if it is something that I don't currently eat much of anyways-if someone tells me I can't have it, then I'll want it.
So, in my low calorie diet, I allow for a small "treat" a couple of times a week-whether it be a sugar free hot cocoa, a little air popped popcorn, or a couple Hershey Kisses one evening. I exercise portion control, and keep it to around 150 calories or less per day, but it is just enough that I don't feel deprived. I believe that it is the same principle in these Prevention diet plans-you are more likely to stick with a plan long term if you have a small indulgence regularly.