But that is the way it has to work. The preview file shows all of the adjustments that have been made using Lightroom. Lightroom doesn't apply changes to the original images. If there wasn't a preview than every time you load an image a new preview would have to be generated from scratch, and that would not be very practical. The preview files are much smaller, and you can choose from different preview sizes.
|Hot Air Balloons Over Bagan by User9320321874|
|Blue mood by darub|
from Fixed lens shootout.
|Yellow Warbler by LeeS|
from A Big Year - birds
|Waiting for the Parade by tcoker1103|
from - La Vida Loca - (Black and White Street Photography+ A Border)