I tend to agree with Andy, the mining boom will have kicked down the average age of cars too.....
I don't dispute that there will be other factors at play. I found the graph interesting none the less. Unlike Europe, we don't tend to crush perfectly good cars just because they're old, the only reason they get scrapped is when they're broken.
One thing is for sure, I'd hate to be a Mini owner
http://tradeinqualityindex.com/vehicles/MINI_Cooper.html
The black line represents the industry average. So of all 1996 build cars, 30+ percent of them have had significant issues (not really a surprise), Mini Coopers have already reported nearly as many failures despite being ten years newer.
If you've got an old tech 95 Jeep (pushrod engine from AMC of the 70's), only 12% of 20 year old cars have reported failures, funnily enough, there's a big drop in problems when Jeep ditched the Renault manual trans. There's another jump in problems when the new V6 was released. Happily, I've got one of the 5% cars, it will run for ever and not cost much if it does go wrong (I could get a engine & trans rebuilt professionally for the cost of a TDI head).
OK, I'm picking on the worst car in the survey, but if you look at the industry average I'd consider nearly 10% failure rate for MY2010 in the subcompact category pretty alarming, especially considering these are more basic American market cars. The only significant diesel car seller VW scores equal last of the volume sellers.
Finally, these figures don't tell the whole story. Reliability isn't just about break downs, it's about what a failure costs to fix. If you want to rebuild an old C4 transmission, it might cost you $2000 tops, so on an ten year old car, that's a completely reasonable spend. No ones going to fix a ten year old DSG or ZF 8 speed if they go bad. Both count as a single failure, but the newer one goes to the crusher (which mean no more failures recorded for that model! - Isn't that handy).