I am part of a WLS family - hubby, MIL and I have the band, FIL had gastric bypass. We all did it within 6 months of each other in 2010.
I can tell you that in the beginning the weight will fly off with just limited portion sizes and by adjusting the band. Then you have to figure out to eat better food, and exercise. My MIL lost about 50 lbs but honestly is lazy about it and not tracking what she is eating in any way, and not really exercising. She floats in a pool like once a week. She lost 50 lbs and that is a great result considering the effort she puts in. She not psychologivally willing to adjust the band as tight as she should because she is not ready to let go of eating larger amounts. So anyone looking at her 2 years out will say she is not successful, as she has about 80 lbs excess weight. But she is not putting in effort.
My husband is the same way except he has adjusted his band as much as possible and he is not willing to change his eating habits or exercise. He lost 120 lbs and has about 80 to go.
I had 95 lbs to lose, have lost 76.5. I watch what I eat 80% of the time. I don't track what I eat, I just make good choices most of the time. I work out 4-6 days a week for 45 min or an hour at a shot. I am very pleased with my weight loss. I know it's not coming back. I can maintain it. I have a metabolic disorder and I feel I am beating it now.
My FIL lost 140 lbs with bypass in 6 months, he is at goal. Had horrible complications for life that can't be addressed. Seeing him go through that constantly reaffirms my decision to get the band.
So if they say lapband only loses 55% of excess weight, it's not that they can't get to goal, it's usually "won't". People are more in control, which often leads to people doin what they want...