I just moved from Melbourne, AU to Las Vegas, and its incredible. I have a running joke with friends back in Australia that you can go out for lunch in Vegas and buy a house with the change.
Having said that, I wouldn't trade my place in Melbourne for any number of houses here :)
Another important point which makes buying cheap US houses unattractive is that being a landlord is a much less attractive prospect in the US.
Being a landlord in Australia is just a matter of wandering down to your local LJ Hooker, handing over the keys, and watching as money starts magically appearing in your bank account. If you buy a block full of cheap houses in Las Vegas you'll be lucky if you can find an agent willing to manage them. If you do, you'll be lucky if he can actually rent 'em out. And if you do rent 'em out you'll be lucky if your tenants don't rip all the wires out for the copper and vanish across the border.
The trouble is, you'd have an easier time selling the scraps of your lunch than you would a home in Vegas. Condos that were going for $180K in my old neighborhood are now at $30K and still going down. It's going to be a looong time before the city recovers.
Having said that, I wouldn't trade my place in Melbourne for any number of houses here :)