Would a koala break immersion?

I had this great idea for a blog post yesterday, but forgot it before I had time to write it up.  So you got a half drunken ramble about how I dig the Castlevania games last night.

Waking up refreshed, I remember!

I was wondering why there aren't many Australian animals in the Monster sections of D&D products.  No kangaroos, no dingos (although the blink dog is described as dingo-like), no wombats, no cassowaries, no frill-necked lizards, no bandicoots, no Tasmanian devils.

The standard D&D milieu has a mix of European, Asian, African, North American, and South American animals.  You can find all kinds of animals from these five continents in a standard D&D wandering monster list, often jumbled together.

Monsters also range in source.  It's no problem to have a minotaur lair near a troll, with an oni (ogre mage) around the bend, and the PCs summon a djinni from a ring to help them battle all three.

Would throwing in a herd of blood-thirsty wallabies really harm immersion in that sort of setting?

And who wouldn't want to use a Giant Carnivorous Platypus in their game?

Giant Carnivorous Platypus
AC: 5 (15)
HD: 8*
Move: 90 (30)
Attacks: 2 claws
Damage: 1d4/1d4 plus poison
Save As: F4
Number Appearing: 1d4 (2d4)
Morale: 8
Treasure Type: C
Alignment: Chaotic
XP: 1200

Giant Carnivorous Platypuses are 10' long, duck-billed, web-footed nocturnal monstrosities that live in rivers, lakes and dungeons.  They prefer to feed on giant insects, but savor the taste of human flesh as well.
A Giant Carnivorous Platypus attacks with its clawed feet, inflicting small amounts of damage, but the victim must Save vs. Poison or die in 1d6 rounds, writhing and screaming in agony the whole time.  Even those that pass the save will be unable to take any actions for 1 round as the poison burns through their veins.
Platypus bills, claws and pelts are sometimes prized by wizards for spell research.  It is rumored that the platypus is a combination of a duck, beaver, and scorpion by a crazed wizard.

Edit--forgot the number appearing!