I, too, was told to expect to lose about half of my excess, which would have been about 85 pounds. I think the reason for the statistics on lap band are due to the fact that your weight loss is still dependent on you. You have to get fills when needed, you have to choose the right foods, and you have to move your body around more.
I told my surgeon at the time that I was a VERY determined person who just never felt full, and that if the lap band would supply that one thing for me, that I would lose all my excess weight. Less than one year later, I am very close to doing just that!