The problem will be trademark dilution. By getting iPodcast they can argue that Podcast is too close, and sue. This is the basis for the cease & desist letters floating around right now.
You're not suggesting that Microsoft would be quite happy for me to use ZuneCast though are you? All companies try and defend their trademarks, and this one ( iPodCast) is obviously derivative of iPod (which is great name for a trademark) - I can see how
it would go too far though.