this is a limitation of iOS. iOS only give third party apps access to the camera roll so basically the app can only pictures and video that was shot using the iOS device. third party apps do not get access to the music or movies. You can copy the music and movies to the WMD and you can access it there. below is a KB article explaining how DRM movies and TV shows will work with the WMD.
http://kb.sandisk.com/app/answers/detail/a_id/12179/kw/wmd%20itunes
