The Knowledge is a real thing,
I think its another case of technology being ahead of legislation. The idea of the black cab rules was not to give a few guys a privilege for nothing. By insisting that they pass the knowledge people know that they will be driven by someone who knows where they are going, the quickest route in the current traffic conditions, and alternatives if there are accidents. Now a good sat nav with real-time traffic updates will do the same thing. Perhaps the need for the monoply has gone now.