Every song in the world is not available thru a consistent API.
A standard, local service should index or otherwise present access to any song I want to play, opening the door for many interesting desktop and web apps that help me organise and discover new music.
you mean a push framework for playdar? so, napster?
not necessarily, just that playdar should be able to find you a way to play any song ever. with enough services hooked up to playdar with resolver plugins, this is possible.