Personally I wish they all were. I love music, but will almost never play a radio outside. We have neighbours at both family cottages that play music and everyone has no choice but to hear it, truely inconsiderate.
Is it common in the US parks to have radios playing outside? I hope not, we are planning a 5 1/2 month trip with 4 months in the South West and Western States and I would hate to be hearing a radio all the time.
I believe most Provincial Parks in Ontario are radio free, but the private campgrounds will vary. Some don't allow alcohol, bottles or cans either, but that is mostly for interior camping from a canoe or hiking.