I realize that on Slashdot, where people tend to be highly math-oriented, it's a popular fallacy to believe that a calorie is a calorie is a calorie. However, studies like this one have been coming out for years now showing that that's simply not true.
Amen. As you say, some foods are more difficult for the body to extract calories from. The body will end up extracting (roughly) the same number of calories from foods with the same caloric content, but the rate of extraction differs, and this can make all the difference. That's one of the ideas behind diets like the South Beach diet: it tries to avoid insulin spikes, which helps control hunger, which helps dieters resist over-eating. Insulin spikes cause all sorts of interesting physiological reactions beyond making a person hungry, such as fatigue, and can contribute to the development of diseases such as diabetes. While not the cause of all the world's woes, insulin spikes (and the foods that cause them) are good things to avoid unless, you know, you suddenly need to outrun a bear. If you're being chased by a bear, by all means suck down that energy gel. And don't bother running downhill; that's a myth -- bears can run downhill as fast as they can uphill, and they can run up to 37 miles an hour. So the bear will still get you, but at least after eating the energy gel you'll taste a little sweeter for the bear.
140 calories from a can of coke is not equivalent to, and will not have the same effect on your body, as 150 calories from 1/4 cup of steel-cut oats. Your health will be better for eating the oats. I don't know whether bears prefer coke or oats; they probably prefer coke, but don't quote me on that.