Playing starcraft 2 soon, so my post is going to be brief (in fact, I'd argue starcraft 2 is a weight loss tool as I eat less while playing it - just like crack!).
What you're saying sort of is true on a traditional diet that we evolved to eat. But that's not the case anymore. We've got mass production of the germ of grains and we mass product high fructose corn syrup and inject it in everything. We treat our food with antibiotics, treat ourselves with antibiotics, and don't eat fermented foods anymore - destroying a tradition of symbiotic bacteria in our intestines.
Insulin is the primary fat storage hormone. The body makes insulin in response to high glycemic load/index carbohydrates. It also makes a lot if the liver is overloaded with fructose. When insulin is high due to poor sensitivity, body fat cannot be used. The body prefers more food as it's source of fuel instead.
Leptin is the hormone that is produced by body fat that goes to the hypothalamus and tells it to stop eating and burn more calories. When leptin doesn't reach the hypothalamus because the hypothalamus doesn't respond (inflammation - probably due to grains, lack of good bacteria, & fructose), our body increases appetite and reduces metabolism. So your calories in - calories out equation is sort of correct, but it's the hypothalamus that's controlling it.
Grumble posted some information on ASP, a fat storage hormone from dietary fat, but the information didn't seem complete. It suggested that people with poor intestinal health & poor insulin sensitivity over produced ASP, so the causality is unclear.
References? There's at least 50 of them in my previous posts in the last 15 pages.
Also I'd recommend reading "Good Calories, Bad Calories" &
Whole Health Source on some migration studies. Time and time again, native cultures eating their traditional diets were documented by the British Empire as being devoid of cancer, heart disease, & diabetes, but as soon as they were given western food, the diseases exploded.
Basically the problem is that western food breaks the metabolism - both implicitly in controlling calories out & hunger for calories in.
Does using willpower, counting calories, and doing cardio work? A lot of times yes, but it sucks. It's not fun, and long term you're probably going to fail, unless you're using it to prevent a broken metabolism. Getting out of the ditch is another story.