As Ohiogirl mentioned, the amount of debt a person might have.....or not have.....skews the "70%" number dramatically. Retirement will generally force a change in living habits for most people, unless you've got a great pension and/or tons of savings and investments socked away. You start thinking more about 'necessities' versus 'blatant frivolous spending' and so on. Those who don't might run into issues on down the road at some point.
So just work the numbers based on your own scenario and go with it!
Bill