That is, lots of European countries cover their entire populations with a budget of around $2000 per citizen per year. Medicare/Medicaid have a budget over $2000 for every citizen per year -- 300 million people * $2000 = $600 Billion.
(In 2010, Medicare had a budget of $453 Billion, and Medicaid has $290 Billion.)
When people call Medicare efficient, it may mean "they spend little money on overhead," but that's very different than spending it well.
What I mean is, when people say "Medicare costs the US more per member of the population (covered or not) than the UK, even though it only covers 1/6th of the population" the stat is unfairly biased - because the segment of the population that medicare covers is the segment that requires by far the most healthcare.
The stat would be dramatically improved if we accounted not by percentage of the population covered, but instead by percentage of healthcare resources used.
This isn't to say that the system isn't massively inefficient, just that it's maybe not quite as bad as that stat suggests :-)