I can't believe you people have managed to go on for a full 2 pages about the consistency of fast food soda dispensers.
Oh come now! You sure as hell can, or you don't know us as well as you think you do.
Joph pretty much hit the exact points I was going to say (or repeat, or resay, or whatever). Every system I've ever worked with used compressed CO2 and worked on a vacuum pump type of deal. You don't change the syrup boxes until they start making crazy noises cause there's no syrup. It takes like 10 seconds to change them anyway. The vendors adjust the brixers, and while it's possible for some owner to decide to tweak with them to save himself a couple bucks a month, usually if they're out of whack it's just because they get out of whack every once in awhile. I suppose if the guy pouring the drink doesn't pay attention, it's possible to give a customer a drink absent sufficient syrup (right when the box goes dry). Usually, it's noticeable though, but never underestimate the incompetence of someone working the drink station at a fast food place.
The only thing I really have to add is that the whole "with or without ice" thing Alma's trying to make a big deal about only exists at the fountains that the actual employees use. They may have a button that is calibrated for different size cups. And they'll dispense an amount which assumes a preset amount of ice has also been put into the cup. So yes, if you order your drink with no ice, you will not get a drink that's filled with soda, but one that's the same amount of soda, just with less ice. But this isn't because of some evil plot by the owner to screw you out of that tiny bit of soda, but because the employees are assumed to be too stupid or incompetent to operate a soda machine properly. That's what the buttons are for.
The fountains in the customer area don't have those buttons. If you want a drink with no ice, there's nothing preventing you from filling it all the way to the top. If saving that tiny bit of syrup was really worth doing, those machines wouldn't allow for free flow of the drinks.