Ping shouldn't be an issue. Battle Servers take care of that nicely, and being an RTS doesn't hurt.
I have no idea whether non-Americans or Europeans are excluded per se. I think it's more that the events are simply based around those timezones, so you can probably still participate. It's likely just the lack of high level Australian players available.
A tournament doesn't require many players. Australia could easily provide enough, especially since almost no one would be scared off by any famous names.
Observer time zones could be an issue, but that can be planned well over a weekend. And casts can also be watched later.
Organising a tournament doesn't necessarily have to be all that difficult either. I haven't personally looked into them all that much, but it seems like the prizes are generally just offered by people who love the game, rather than business sponsors. A couple hundred dollars isn't really all that much (if you don't have kids

). Prizes can also be crowd-sourced. I'd probably enjoy running one. My main limitation is my slow upload speed which limits casting quality heavily.