You'd be surprised how many average joe's earning a 100k have 600k mortgages with their partner. One full wage goes on the mortgage and other to spend and live off. Not even thinking about paying it off just servicing the mortgage every week to keep up with a certain lifestyle.
I think what people forget when the go to get a loan is......The banks don't do the worrying for you they really dont give a crap if you lie or fudge figures to get the amount you need, they have their end of the bargain covered by the government and the tax payer.