Duty free scotch whisky

I often travel from Vancouver BC to Washington State, and often stop at a duty-free store on the way home. I have noticed that the quality of duty-free scotch is usually less than what I would purchase in liquor stores in BC and Washington. Usually such duty-free scotch has a more grain alcohol taste than the normal product. (Even discounting any difference in alcohol content.)

For example, several bottles of duty free Johnny Walker Black Label, and of Chivas Regal 12 year old. I currently have a bottle of duty-free Glenfiddich 12 year old and am fairly certain it is not of the quality of liquor store product.

Has anyone noticed such a difference between liquor store whisky and duty-free?