More detail from the NY Times:
http://www.nytimes.com/2008/02/29/us/29walks.html
I think this paragraph says why so many people are in trouble:
Last year the median down payment on home purchases was 9 percent, down from 20 percent in 1989, according to a survey by the National Association of Realtors. Twenty-nine percent of buyers put no money down. For first-time home buyers, the median was 2 percent. And many borrowed more than the price of the home in order to cover closing costs.
All I can say is my monthly mortgage would pay for a pretty nice bike.