These cars are not perfect. Remember also that the way that height is adjusted on these cars means that if the car is weighted unevenly the adjusters will end up in different places to put the car at the same height. So if your car isn't perfectly balanced, and very few of them are, then you'll end up with different adjuster settings. So having different adjuster settings is probably more common than having them be exactly the same.
A 1/2" is kind of a large amount though. Do you have SS springs on the car? If you do, you're probably compensating for the difference in the SS springs to level the front of the car.