Wow...
Cheers Raymo...
Here in Cairns we have the Rainforests & the associated tropical flowers, etc... which are pretty awesome in themselves but, the spread of rainforests is limited to quite a small region really..
Not that I'm any kind of expert (or even particularly knowlegeable for that matter) but, I'm guessing the spread in WA relates to a fairly stable climate across the wider area of the state... Having been there a few times, I know there is still considerable variation between say Broome & Margaret River but, it seems to be a little less dramatic than say between Cairns & say Melbourne, if you get my drift..
Of course, I could be completely mistaken...