It might be unique to The Netherlands then, but eveyrbody pays the same for a single ticket at the door no matter your country of origin.
I suppose that is the same all over Europe (at least Northern Europe), but maybe I am wrong.
What they normally do is sell yearly memberships. One time entrance is say 10 euro's, or you can come as many times as you like for a year for the total sum of say 50 euro's. That way the local people can enjoy the attraction for a lower average price, but there is no dual pricing (which is against the law). In Holland you buy a museum year card and you can enter 200 musea for a year for like 100 euros. Visit 5 museums and you got your money out of it already. A similar thing I see here in Thailand as well: the aquarium here on Phuket sells a yearly membership for 999 baht where a regular ticket is about 100-200 baht. A waterpark sold tickets for 500 baht, or you buy a yearly membership for 4 people for 25K baht. Come once a month and you are better off with the yearly ticket, but for tourists it is not worth it as they are only here for a couple of days/weeks.