I think all that is simple empirical observation and a little common sense. But this leads to another question: are all cultures and nations equally gifted musically? According to the doctrine of multiculturalism, the answer should be yes, the cultures of all nations are of equal worth. But this seems incorrect to me. For example, some nations have enormous and brilliant musical traditions while others do not. Take Italy and Switzerland, for example. Though next door neighbors, one has an unequaled musical tradition but the other does not. Italy has given the world opera, Vivaldi, Verdi, Rossini, Francesco da Milano, Stradivarius violins, La Scala, Pavarotti and the list goes on and on.
OK, now name one important composer from Switzerland.
See what I mean?
In Latin America there are strong musical traditions in some nations like Argentina and Brazil, and very scanty musical traditions in other nations like Chile and Bolivia. By "scanty" I don't mean that there is no music--there is scads of music--but that little of it is of lasting quality. Mexico, where I live, seems to be a somewhat tone-deaf nation. True, there are some fine Mexican musicians like the composer Manuel M. Ponce or the singer Luis Miguel, and the mariachi tradition is an interesting one. But by and large, Mexican music is harsh in timbre and rhythmically stiff. Brazilian music, on the other hand, is typically fluid and charming.
Why is this? I'm not sure. The reasons are probably complex and different for every culture. One interesting phenomenon seems to be that oppressed sub-cultures sometimes develop strong musical traditions. Some that come to mind are the gypsy culture in Europe where the gypsy folk music traditions are very strong in places like Hungary, Romania and Spain. Flamenco is largely the creation of the gypsy culture of Andalusia in southern Spain. Another one is the Irish musical tradition, a Celtic one that has lived under English domination through most of modern history. A third one is the Black music culture in the US which has given the world blues, gospel and jazz.
How about some examples? First, Guinness-fueled Irish fiddling and picking:
Next, one of the original Delta bluesmen, Charley Patton with "Spoonful Blues":
Here are the virtuosic Romanian gypsy band Taraf de Haidouks:
You don't hear that kind of thing every day...