I find questions like this difficult to assess because each of us have our own experience as our most prevalent reference point, and yet we change over time as well. For me, radio has made a series of missteps that has made it totally irrelevant - to me, anyway. There is absolutely no reason to listen to it, and many reasons to not listen to it - the music selection is terrible, there are commercials, you have to listen to an announcer, etc. It's so easy to have your choice of commercial-free music of your choice and variety anywhere you happen to be going, there's no reason to listen to radio anymore.
I agree that the incredible quantity and diversity of music coupled with a lack of adaptation by the people marketing music have led to the "decline". The music industry is responding about as slowly and ineptly as baseball is responding to they're problems - so slowly, you can barely perceive it. While I don't support piracy, and in fact am an incredibly good customer of the music industry, it's pretty obvious why piracy occurs and that it will continue to occur until the industry starts to make fundamental changes instead of the little tactical ones they're currently taking.
