I suppose that P2P file sharing will eventually end up doing away with "major labels" and the RIAA. The major labels and RIAA just had a lot of money and contracts to begin with. The influence lent them by the money and contracts (lobbying, PR campaigns, law suits) has let them hang on for a while, as file sharing nibbles the foundations of the business from under them.
There's also clearly a societal component. We believe that "artists" own the music, even when legally, they may or may not. The PR campaigns referenced above tend to support societal concepts like "owning" ideas or riffs or sequences of notes. It will just take a while for the population who believes in owning ideas or concepts to turn over.
In the meantime, the RIAA thrives.