I do WW and nothing is "free" -- there are many vegetables that are considered "free" -- as in you are allowed to eat what you want, but even with these, if you want to eat a whole head of lettuce, you have to start counting at some point. I think their plan is to get you to make healthier choices, so if you technically go over your daily points (1 point equals approximately 50 calores) because you had a "free" salad -- okay -- but you can't have "free" cookies or anything like that!!
Besides, with the "negative" foods -- it seems like even if it was true, who wants to spend that much time calculating how much work it took to chew/digest everything? To me the point of tracking calories/points, etc. is to make it easier for me to keep track, without obsessing over it.