In an interesting coincidence, Europeans outnumber Americans approximately 2.4 : 1 (730 mil to 300 mil), so maybe there exists a simple explanation for this phenomenon...
You probably took that number from Wikipedia, where Russia (100m) and Turkey (80m) and many other unrelated countries count as Europe too. The exact number for today's EU is 486m.
Paul, you have theories about everything, how about this one? :)
There was an interesting article about why jazz is more popular in Eurpoe and Japan than in the U.S. Accoring to the author, it was something to do with abstract thinking: if music is a language, then jazz is the most abstract part of it - no feelings, no relation to real-world notions, just pure musical math. (I'd say also baroque music is as abstract as jazz.)
SecondLife in a way is about abstract thinking, too.
It seems to me the most likely explanation is that Europeans care more about liking highbrow things. Most people who like jazz are also rather proud that they like it.
I suspect you'd also find more Europeans than Americans are fans of Beuys, or Lacan, or Finnegan's Wake, or other such things that might have been created as controls in experiments to measure pretentiousness.
I did some research on Flickr some time ago and it turned out that Flickr is European-centric too. Is photography as a hobby a "highbrow thing"? In a way, yes, but the opposite of that is countless crappy "three of us at a barbeque party" pics. Given a choice, I'd stick to those pretentious hobbyists, because creativity is pretentious by definition. (But not everything that's pretentious is worthwhile, of course.)
Music itself is an abstract language indeed, but over time it developed so much that composers were able to express human feelings, emotions, as well as create associations with natural phenomena. One such example is Vivaldi's Four Seasons (though Vivaldi himself was a baroque composer, but this particular piece was probably one of the first notable experiments in this regard).
I don't think anyone would argue that, for example, Bach's Well-Tempered Clavier has any association with anything at all. It's pure math and nothing more, yet we may enjoy it "as is".
Speaking of jazz, perhaps it would be more difficult to prove that jazz to pop is like Bach to Beethoven, for instance, but there is some truth in it. Take Miles' music, or Monk's or many of their followers, their music is much closer to the musical math than to anything else. No wonder the names of their albums and tunes are often rather meaningless (e.g. "This is jazz No.17").
What I'm trying to say is jazz is more abstract than many other genres. Appreciation of jazz, and the same I believe applies to Bach's music as well, aside from Paul's thesis on pretentiousness, which is true :) does require some abstract thinking.
But... let me stop here, because it would be even harder to explain (if possible at all) how this all relates to SecondLife and Flickr.
I'd maverick and say that the Well-Tempered Clavier is full of metaphors. Consonance, dissonance, ascending sequences, descending sequences, 'voices,' and subjects are all human, intuitive associations and descriptions of music. Music has had active metaphors ever since natural language was used to describe it.
But you're right, this is getting really off-topic and comparing Jazz to mainstream Pop is at least O(JP). So I'll just link an Essay that came to mind the first time I read "Taste for Makers." It's similar, but takes an "only the best audience matters" point of view.
