I won't argue that calories ultimately matter, even on low carb. However...our bodies are more complex than people want to give credit for and there are a host of factors that ultimately determine what a good calorie level will be for each individual, including (but not limited to) hormone levels, activity levels and age. One size does not fit all.
What if....eating one way naturally made you burn more calories during an average day than another simply because your body had to work harder to break down those foods into energy and the metabolic pathways for doing so were less efficient than others? Wouldn't you be able to eat more calories eating this way, and still lose weight, than in another fashion where the metabolic pathways for breaking down those foods into energy were much more efficient and therefore less energy was wasted in the process of breaking chemical bonds?
I won't argue that low calorie diets work, but at what cost? And...how sustainable are they for the long haul? How easy (and realistic) is it to stick with a program when you are hungry and your body is crying out for food? Hunger is a very powerful drive and to expect people to override that drive consistantly is unrealistic at best.
I agree that many people have tried Atkins or other low carb programs and failed. Is this design flaw or operator error? Trying a program for a few weeks and giving up when the weight doesn't come off as fast as you'd like is very different from sticking with a program for a decent length of time (more than 3-5 weeks) and giving your body a chance to rest when it needs it.
I disagree with the statement that many (if not all) people stop losing weight after 3-5 weeks simply on low carb diets. My own experience (as well as hundreds of others here on this board) after 18 months on low carb has proven that to be false. Granted, I'm losing at a slow pace, but this isn't a race and I AM still losing. Plateaus and stalls are common in all forms of dieting, even starvation.
Then there's the issue of insulin resistance. High levels of carbs contribute to that problem and this has been demonstrated scientifically. Diabetes (which means you are insulin resistant by nature if you are a type 2) is reaching epidemic proportions both in the US and in other countries. Why? Apparently DIET COMPOSTION does matter for some, likely many and should be the main focus for people who have this medical problem. Okay....so carbs are a problem for those with insulin resistance. What does that leave? Low amounts of carbs in the form of low GI veggies, fruits and nuts, proteins and fats. Sounds like low carb to me.
One more thought...if low fat/low calorie diets work so well, why are people getting fatter following them? Design flaw or operator error?