Even though the drinking age is different there are really strict laws about Alcohol at customs. You have to be 21 and you may only have 1 litter of alcohol, they do consider perfumes and other things with alcohol in that figure.
That is crazy, are you saying if you have perfume and other things like that then they are going to count them towards the total amount of alcohol you can have?? Why?
Perhaps it has to do with being a vacation spot? And they don't want people getting too crazy and making it unattractive or dangerous for people to visit?