It's hard to say whether our standards are lower, they're definitely different
It does suck that our seats don't rear-face longer (although saying that, there would be a trade-off with needing bigger cars really - in the US, for example, I'm pretty sure the avg 'family' car is bigger cos their seats are HUGE, we certainly wouldn't be able to fit 3 carseats in a Ford Focus like I can here), and that we can only use a 5-pt harness up to 18kg, and boosters up to 26kg. BUT the actual standards on our seats themselves are higher, if that makes any sense (which is why you can't use a seat here that doesn't meet Aust. standards, even if it *seems* safer, I guess we are not the experts!)
One would think manufacturers would work out something better, but there ya go.