Death of the 'Concept' Album? From Revolver to There's a Riot Goin' On to Kid A, rockers have prided themselves on concept albums that promised meanings bigger than the sum of their parts. But the advent of Internet downloading has created a Darwinian world in which only the strongest tracks survive. What's happening to the notion of an album as a cohesive work of art? NPR's Neda Ulaby reports.