We often think organic means fewer calories, and that's why we should institute mandatory calorie counting.
Let's say you're at the mall, and someone offers you some food samples—cookies and potato chips. They're labeled “organic” or “non-organic.” Except this is really just an experiment and all the food is organic, but you don't know that yet and they're asking you what you think about "organic." If you're like most people, you tell them the "organic" food is healthier, tastes better, and has fewer calories.
So while the jury's still out on whether organic foods universally have more micronutrients, the study suggests that organic foods have a discernable “health halo,” which means consumers might think they can eat more organic foods—even if cookies and potato chips are neither healthy nor nutritious—because of some perceived health benefit.
Wansink has found (PDF) a similar "halo bias" when people ate at Subway, a "supposedly healthy restaurant." In that case, Subway consumers chronically underestimated the number of calories in their meals compared to those eating at McDonald’s, regardless of their meal size.
The bottom line is calorie counting certainly has shortcomings, but, without clear, concise information about the caloric content of meals, people draw all kinds of conclusions from other cues—whether or not the food served is actually healthier.