again pretty much what Ermz said. The issue is, as he stated, there's no where to go if you're good here. Like... you get to a point where you are really good, you play to about 250 people or so on a really good night, you do the rounds through australia.... and that's it... there's no real support network here, no way of being promoted very well at all...
So we all start looking overseas, it tends to work out much better much sooner. There's legions of bands around Australia who've been at it for years, and are at that point of being a "good" aussie band, and then you ask anyone OS and no one knows who they are. It's a shame really..
Just to plug some:
Eye of the Enemy
Anno Domini
Orpheus
In Malices Wake
Belakor
Not deathcore, I'm sure others can chip in for them