This discussion reminds me of one of my favorite speeches from Tom Stoppard's "Arcadia":

"We shed as we pick up, like travellers who must carry everything in their arms, and what we let fall will be picked up by those behind. The procession is very long and life is very short. We die on the march. But there is nothing outside the march so nothing can be lost to it. The missing plays of Sophocles wil turn up piece by piece, or be written again in another language. Ancient cures for diseases will reveaal themselves once more. Mathematical discoveries glimpsed and lost to view will have their time again. You do not suppose, my lady, that if all of Archimedes had been hiding in the great library of Alexandria, we would be at a loss for a corkscrew?"

(notice in this metaphor that the future is behind, as was discussed on another thread at this site)

Aren't hiphop sampling techniques similar to what 13th-14th century composers were doing when they blended chant fragments and popular songs into polytextual motets? Then there's the cantus firmus mass--how many Renaissance composers embedded "L'homme armé" into their Mass Ordinary movements? How much Motown is embedded in CCM?