The easiest way I find to think about it is to think about the Innocent Smoothie adverts (if you haven't see them, YouTube it!). They show you how much fruit goes into every carton (loads!) - most people could probably drink a whole carton pretty easily, but would probably struggle if presented with plates full of the 'raw' fruit.
Although pureeing or cooking doesn't change the nutritional value, it does change how much you can eat without trouble, and therefore increases your calorie intake. Also, it's digested much faster than 'raw' fruit, and so you feel full for less time (so more likely to snack).
Hope that helps a bit...