@Maksym **********
In the case of Australia and New Zealand, they should be exempting their own citizens. Other countries do this. Even the USA wasn't requiring arrival forms for their own citizens while foreigners had to fill out the white or green I-94 forms (depending on whether they were coming with or without a visa).
So yes, it's discrimination because Aus/NZ citizens aren't being given any special privileges despite the fact they are citizens and thus should have more rights than foreigners.
In Thailand's case, the arrival form isn't required for Thais, which is the way it should be.