Howard et als rationale on debt is that it is offset by rising asset prices (ie the greenspan explanation), however there is a key differences in debt levels - see table;
Household Debt as % of GDP USA UK Australia Europe Japan 1988 57.9 66.6 36.8 Na 59.7 1993 62.2 74.8 42.9 Na 63.3 1998 67.1 72.5 61.2 41.7 65.1 2003 83.5 91.8 100.3 48.3 67.3 Source: Morgan Stanley