Say we count a person's languages fractionally, based on fluency. Roughly speaking, 0.25 is what you need to get by as a tourist, 0.5 is enough to get a job and live there for a while, 0.75 is what you need if you want to converse socially or find a date, and 1.0 is true native fluency (including both spoken and written).
From what I've seen, the average number of languages spoken by continental Europeans is in the neighborhood of 2.5.
And the average number of languages spoken by citizens of the US is about 0.8.
Either that, or they're fluent in some language other than English that I haven't heard about. :-P