Arbitrage I'm sure affordability is not meaningless to the large proportion of borrowers who pay a substantial proportion of personal income just to live in a home.
I've recently moved back to Auckland after a year away in the (not so) winterless north. I'm not renting the same house that I rented when I left but there isn't a material difference in the rent I'm paying yet property values are about 10% higher (REINZ and RBNZ statistics tell me that my rent is actually around 3% higher but the house is worth around 12% more - 'course the stats are skewed by reporting what is selling rather than what your house is actually worth but it provides an indicator).
Now in any market where I've participated there is a name for low income growth and high capital growth and it isn't great fundamentals. The same trends appear when comparing house values with incomes. The trends are simply not sustainable. A well known property figure was recently quoted as saying house values will double in the next 10 years. This is easily achievable if incomes also double. A dubious value proposition if they don't. At some point in the property pyramid you need someone who can buy your 350 metres of suburban paradise. At 9% fixed rates the average Auckland house price is now costing around half the average joint medium income (pre tax!). Ask those poor sods if affordability is meaningful or meaningless?