I almost never get McDonald's in the U.S., but since the concept of fountain soda - not to mention putting any visible amount of ice in a cup - is almost unknown here, I dropped by one after a long walk today.
First of all, when you order a soda, they assume you mean soda water. The fountain looks like it does in the U.S., only with a smaller, separate ice dispenser. I pushed to get some ice, and about 5 of the little McDonald's style cubelets came out.
I figured it was out of ice and reluctantly gave up. But no, what actually happens is that you push for your 5 cubelets, let it go, then push again to get anywhere from 3 to 7 more cubelets (in my limited observed dataset). I don't know if this is to frustrate customers into just not getting much ice, or an assumption that most of their customers only want a tiny algae bloom worth of ice on top of their drink. Either way, I'm onto their little game now.