This really blows my mind...I always assumed a vehicle could not be sold in the US UNTIL it was tested both by EPA and NHSTA. Silly me, I thought Big Brother was watching out for us.
Anyway, the VE Commodore on which the G8 is based: "Crash test results from ANCAP rate the VE lower in the offset frontal impact test than the previous generation Commodore. The overall crash score was marginally higher than the outgoing VZ, due to improvements in side impact protection giving a score of 27.45 out of 37 or a four star rating out of a possible five."
If you look at interior shots it looks like the G8 has been highly modifed to suit US regulations. I guess the Aussie based VE Commodore does NOT have to be designed for people not wearing seat-belts but the G8 does.
As an update the latest ANCAP results for 2009 VE Commodore give 5-stars.