This has been on the horizon since the Copyright Board raised the mechanical license fee by about 1000% and Congress refused to act. There have been various settlements for various sized webcasters. But the utter refusal of Congress to deal with this issue is having what some of us predicted would be the result. Whatever survives of internet radio will be tamed by the big labels, because they have all the leverage in the negotiations.
Ah well. It was a nice idea while it lasted.