The article in question is actually comparing the EU (rather than the continent of Europe) vs the US which are both single markets, so discussion about flights to Moscow or Istanbul should really be excluded.
To that extent, the EU and the US are both "big". EU land mass is 4.3m sq km and 500 million people. US land mass is 9.1m sq km (including Alaska as has been pointed out) and 310 million people. I think it's fair to say that these are both big enough to create economies of scale. Despite the smaller population, the US should have an advantage in this as it has been a single market for a lot longer than the EU.
My own personal experience suggests the article is roughly correct but as florin said, we are trying to compare apples and oranges and I suspect that this really reflects my own personal travel within the US vs that within the EU.
Of more interest to me would be an article on why the American consumer gets absolutely fleeced on TATLs originating in the US vs. what the European consumer pays ex-EU but no doubt someone will be along shortly to defend US "free enterprise" (sic).