The statue of liberty/wtc is somewhat of a silly point of comparison for national debt but grounding numbers into something familiar or in this case physical objects is quite telling for most people. Even if your point of comparison is "the federal budget/GDP/world GDP/debt of other large nations" it goes back to the same issue where you are comparing large numbers to other large numbers which is meaningless to most people(outside of HN). I wouldn't use this type of visualization to brief congress but it is telling.