Is there any compelling reason why we can't get this in Australia?
Because this is the arse-end of the universe! We're too far from the existing satellites and the $$$ it would cost to cover Oz vs the number of likely users makes it unviable. I believe that if you have the kit and the subscription that it may work on the east coast of Oz due to overlap from pacific satellites (I'm sure I read that somewhere).
The other factor is the quality of the information it gives. I don't know how/where they get the info from in the US but assuming it here it would rely on feeds from the BoM, the info available from BoM is a)limited and b)available elsewhere anyway (might as well have a 3G phone connected to a tablet PC - except it's not overlaid).
I was amazed to learn that when you call Centre and ask for radar info on TS, all they have is the same feed that we can see on the BoM website and it only gets updated every 10 minutes as well. They do have lighting strike sensors in Oz but if/how that info would be available to an XM weather provider I don't know - maybe someone else does?
It looks good but simply getting Sat coverage is only part of the issue I think.
UTR.