Thanks to this PowerLine post, I discovered an article by economist Jeremy Rifkin ("Bush must face up to a rising power") in which he warns Americans to stop being so naive:
To a great extent, we Americans and many Europeans have blinkers on. Virtually the entire European continent now lives under a common flag, a single passport, and, soon, a common constitution. But we are still in the habit of comparing Germany or France to the US.
In other words, Rifkin was indirectly warning me that the National Debt Thermometer should show the EU as a single unit, besides separating out Germany, France, etc. So I fixed it. You can view the updated National Debt Thermometer here. (Result: EU debt burden = 78% of GDP; USA still 64%. Source: the spreadsheet below, obtained from the OECD site; highlights mine.)
Thanks go out to economist Rifkin and PowerLine for helping me make the graphic more informative.
Click on the graphic below to view the OECD data table I used.