The DS is a tool, it is not magic. In the beginning, even for a few years, you will lose weight and maintain no matter what you eat (that is true for most of us anyway). But after a few years, your body will adjust somewhat and if you eat excessive simple carbs you will start to gain weight back.
Your relationship with food is going to change over time after the surgery. And if you want to maintain your weight loss you have to watch the carbs. Not like a major "diet" like you've probably done zillions of times, but your carb intake has to be minimal in order to keep the weight off down the line.
The good thing is you will always be able to eat plenty of fat and protein which makes it pretty palatable.
I have a huge appetite, I eat a lot of food. My stomach is stretched as big as it was pre-op. The difference is malabsorption of course, but I do absorb the simple carbs and my body has gotten better at absorbing them over time.
I'm 9 years, 5 months post-op.