As an example - if I get to reduce my mortgage payment by $500 - because interest rate is extremely low - I could technically spend that money on upgrading my car or travel or groceries or eating out - and so pushing up the price. At least that's how I understand it.
I assumed that housing prices were included but apparently not (at least in the US)[1]
[1] http://www.nytimes.com/2011/04/02/business/02charts.html?mcu...