Whenever I hear this sort of quote, I always wonder who originally said it. Usually I imagine it originated with a (socially) conservative white guy, with European ancestry. Given that, it's pretty amazing that jazz makes grade of real "art."
Not only jazz, blues and rock-and-roll spring to mind, but hip hop, jazz fusion, funk, bluegrass, gospel and tap spring to mind as quite distinct artistic pursuits that bear an unmistakable American stamp. In fact, I find it hard to think of a popular musical revelation of the past 75 or 100 years that didn't originate in the US. BUt then again, I'm not that worldly.
But guess what? Apart from jazz (increasingly), these musical forms tend not to be studied extensively in conservatories. This is not surprising, given that they are the "folk" creations of such a young country. But it makes it difficult to establish validity before the court of entrenched art experts.
And what about cinema? Love it or hate it, Hollywood has forged new styles of cinematographic art: new genres, new technical processes etc.
And what about literature? Hasn't American literature done enough to warrant recognition as a different beast from European literature? Could The Great Gatsby possibly have been written by an Englishman?
If you wander the great art schools and conservatories or Paris, Rome, London and even New York, it's likely that you'd find few references to traditions that are identifiably American. For some reason, jazz seems to be breaking this mold, at least in the US. But the curriculums of these schools seems to be a very narrow way of defining "art."
As an aside, something very strange strikes me when I think of the quite amazing range of musical offerings of American heritage. Jazz, blues, funk, tap, hip hop, gospel and arguably early rock-and-roll (i.e. an overwhelming majority of the inspiration for distinctly American music) has come from the African American community. And this, despite the fact that African Americans constitute maybe 12% of the population. I guess the (completely tongue-in-cheek) question becomes "Has white America made any real artistic contributions in the music arena?"
Chad