So, roughly 15k€/person/year or 30k€/couple/year, assume 2-4% wage increase/year and 2-4% interest, it's not hard to imagine 700k€/1M USD/family, especially if the average age of parents in a family is 40-45 (they have been working 20-25 years).
That's good, but that wouldn't be the average family -- that would be the average person
at the time of retirement. 2008 numbers pegged average Australian net worth around $250k. It's hard to go from an average total individual net worth of $250k to an average size of retirement assets at four times that. Plus those averages are heavily pulled down by the fact that most people are not at retirement age, even in greyed countries like the US and Australia (I don't think there's any country where the average 30-something has $1M USD in retirement assets).
In trying to find a comparable numbers for the US, I found a 2010 estimate putting mean net worth around $180k per person, although I found a wide range of estimates.
These are all means, and as such are distorted by income inequality / distribution, but still, I don't see a basis to suggest that the retirement assets of the mean Aussie are 6 or 7 times the total assets of the mean American.
I don't live paycheck-to-paycheck, and I do think Americans need to be saving more, and I also think that a purely do-it-yourself system like the American 401k system is not working, but I'm skeptical of some of the numbers being tossed around in this thread.