I don't think anyone doubts you can lose weight by just eating fewer calories, but part of weight loss is that you have to be able to continue the weight loss (motivation, dealing with cravings, dealing with health issues, dealing with food addiction).
It really beggers belief that people think that fat people just willingly make themselves fat as a willing exchange for eating a few comforting foods. Fat people would rather be thin, and I am sure most (not all but most) would be willing to sacrifice their favourite foods to do so. The problem is, that sacrifice involves a continual sacrifice. It's not a one off thing. The sacrifice also involves willpower, one that thinner people usually do not need to make because they don't think about food the same way as fat people. They don't think about it as often either. Part of this is psychology, but part of this is in no doubt due to physiological response to some of the foods we eat. I am of the firm opinion that fructose and HFCS in particular (known as glucose/fructose syrup here in the UK) is one of the contributing causes of the rise of overweight and obesity. It changes our physiology and that in turn changes part of our mind's view of food. I forget who posted it, but someone posted a very long, but very good video about the differences in sugar metabolism and fructose's contribution to obesity in the Shrinker's thread.
What does this have to do with the Twinkie diet? Losing weight isn't just about taking weight off. If it were, I would have stayed thin one of the first times I lost significant amounts of weight. It requires a lifetime commitment to monitoring your health, weight, diet. It requires a change in attitudes towards food and eating a diet exclusively of something made with HFCS and highly refined stodge is going to do nothing but change that for the worst over the long term.
I also read somewhere that this guy had to keep cutting calories to continue to lose. The "starvation mode" that people talk about generally doesn't last that long. However, when you deny your body the essential macro-nutrient of protein, your lean body mass suffers, and this reduces your BMR. You will be in a semi-starvation mode until you regain that mass.
His numbers look great now, but almost all weight loss, no matter the method (including total starvation) will initially improve things like serum cholesterol levels. I'd like to see this guy stick to this a year, go back to eating normal food (even a better diet than he was on before the "Twinkie diet") and let us see how he is about 6 months after that.
Again, you can lose weight by being calorie deficient. Losing weight in itself doesn't make a successful weight reduction diet for people with real weight problems.
ETA: Jennette Fulda, coincidently, posted something along the same lines about obese people being different than non-obese:
http://pastaqueen.com/blog/2010/11/obesity-as-an-illness-of-metaphor/Stuff like this guy's experiment doesn't make us understand obesity more, but less.