That's why I use Rhapsody and a Sony Video mp3 player over iTunes and an iPod. I can drag and drop music on anyones PC.
The platform is not the issue. It's if the content is DRM'd or not. I can drag unDRM'd content off my iPod to any PC or Mac too.
Rhapsody is DRM free.
Relatively new development, right? Since June I think? Which means all those Rhapsody mp3's will work just fine on an iPod
BTW, iTunes has been offering DRM-free tracks for over a year (not to say that all of Apple's offering are DRM-free but then, that's an issue with the record labels not with what Apple would like to be).