Of course iTunes is the perfect example of that -- everything on iTunes was, and still is, available on P2P networks, but its so much easier just to pay the 99c and get guaranteed quality without spending 2 hours searching for a 3 minute song.
Although it takes 2 hours because the RIAA keep shutting down all the good download sites. If napster were still up and running i'm sure they would have made a rating system (like Digg) for good quality songs and you'd be able to get songs just as easily as iTunes for free.