Corporate America figured out a long time ago that the average consumer is pretty dumb.
"Hmmm...how can I sell you a 24 oz. fountain drink for $3.49 but only give you 12 oz. of product? Yes! Fill half of the cup with ice and then promote the immediate gratification and satisfaction of an iced cold beverage. Cost to me, including the cup, is about 12 cents - $3.37 in profit!!!"
Ice waters down your flavored corn syrup/carbonated water drink and kills the flavor. It also leaves you wanting more since we tend to consume more of less satisfying foods. If it is bland, we gobble down more of it. Food, soft drinks, sugared coffee, booze, beer, etc. - we crave it if it is essentially flavor muted.