From what I've looked into, Safari on Windows isn't using Cocoa. The latest Safari even looks much more like a Windows application than previous versions. So maybe I'm wrong about this point. However, I still think they're going to have to port iTunes to Cocoa simply because they've essentially deprecated Carbon. For the Windows version of iTunes, maybe they'll just have an completely separate version that isn't a port.
I know that when Safari for Windows first came out people were looking into some of the DLLs that were installed along with it, which were ports of things -- IIRC CF libraries at the very least -- from OSX. They may have depreciated those in newer versions due to poor compatibility with Windows.
