Yeah your stomach can stretch if you eat more food, and shrink if you eat less.  That's why as you restrict your calorie intake your stomach slowly shrinks allowing you to feel more satiated on smaller portions.  Lap-band surgery is basically an artificial way of shrinking your stomach overnight, but it's particularly dangerous when people don't take their strict portions seriously (there have been stories on here of people's stomachs exploding after weight loss surgery because they tried to eat the amount they usually eat).  It's also why it doesn't typically work in the long run because they just end up stretching their stomach again because they have made no lifestyle changes and have no idea about portion control.