So do you not get to download the songs? It's just a ad-free pandora? If so, obviously they'll need itunes and the likes because people like to download songs, not just access them over the internet.
Sony needs the income and distribution capability of iTunes at the moment. As soon as the service takes off though, I'm sure they can leverage this against Apple, seeing that Sony BMG controls a big portion of the market.
Personally I'd love to see the competitors (Zune, Sony, etc.) all bunch up together to offer one, big, unified competitor against iTunes.