Incorrect - the average value does double ten years, unless of course you're not in a popular area (Gore anyone?). The only consolidating factor is every recession, which slows it down. However the same 10 year average does tend to apply.
Numerous examples can be given. How much did houses cost for your folks? When did they buy? Do the math, it may just surprise you!
EDIT: Yes it is unaffordable for many! However if you have 2 salaries and if you're good with your money then it can be done. I myself am limited to a $300,000 budget currently - So, I ask you, what can I buy for that in Auckland?