According to the Guardian:
"YouTube users will be able to use music from artists including Led Zeppelin, Madonna and Red Hot Chili Peppers legally in the homemade videos they upload, following a deal with Warner Music.
Under the landmark deal, Warner Music has also agreed to provide music videos from its extensive catalogue of artists on the video-sharing website for the first time."
Warner Music are not doing this for charitable/support Internet copyright abuse reasons - they're doing it for the oldest reason on the planet - money! You see YouTube are about to launch a sophisticated video ad system which means that videos carrying Time Warner music/artists will earn Time Warner ad dollars as they are viewed by YouTube users.
This has to be the monetization (techno coolo smarty pants term) model for videos/TV on the Internet. Get that handycam out - now you can make money off it - finally!