I'm a man who weighs about 200 pounds, has a blood pressure of 120/80, and slightly elevated cholesterol. Growing up, I could eat a box of cupcakes a day (no exaggeration -- 12 cupcakes a day) witout gaining weight and I can still eat quite a bit of junk food and processed carbs. I never really had any sort of attention-deficit disorder, either. My wife has PCOS and can eat substantially less than I do and still gain weight on a traditional diet. Another friend was tested and found out that he'll gain weight if he eats more than 900 calories a day so he opted for a gastric bypass (which I'm not advocating). I know by comparing what I eat and what they eat and by what I weigh and what they weigh that "metabolism" is a very real issue when it comes to how people react to food or gain weight.
The people who complain about "fat chicks" and think that "eat less" is a winning diet strategy are usually people like me who can eat just about anything they want without gaining weight. It's easy for me to diet because I can also just skip meals or eat less because I usually don't suffer the blood sugar ups and downs that create hunger (though I can feel how strong they are when I do have them). Not everyone is the same. They key is to identify your particular problem and find an eating strategy that works for you, much as people might try different anti-histamines or pain medication to find the one that works best for their metabolism. One size does not fit all.
You hit the nail on the head. I believe that most people who do low carb have realized this issue and are more open to the fact that it's a your mileage may vary thing. I personally can't do strict Atkins, but I do have to control *when* I eat carbs. I am doing Carbohydrate Addicts and am having great success because it is what works best for me.
If the low fat diet works for some that is great, if people need to do a more vegetarian diet that is fine too, but it should be fine also for those who need to restrict refined carbs for their optimum health. That is the problem I have with all the nutritionists who insist that everyone must follow the exact same guidelines.
All of my PCOS symptoms have been reversed for the most part since I started low carbing and knowing that the problems were worsened when I followed the low fat diet. I nearly ruined my health long term because of following others advice and ignoring how I felt and looked. It isn't just the weight that was bothering me. That was just one of many symptoms that something was terribly wrong.