It would be outrages if a dive shop told people not to drink the day before diving.The way I read your first post, you are outraged that some dive ops would have this rule, and it would be alienating to Europeans.
They might not care when you just rent their tanks but I doubt there are many ops that let you drink before or inbetween dives when you're on their boat or diving with their staff.... the diving there is shore-based in a rented car.